Skip to contentSkip to conversation

misc: servo-pwm: driver for controlling servo motors via PWM

PATCH In review Angelo Compagnucci 7 participants 10 messages Feb 17, 2023 – Jul 15, 2023

Subsystems (3)
Device tree bindings Char and misc drivers PWM
lore
Share & tools
lore

Angelo Compagnucci

author
#0 lore raw

PATCH v3 1/3 misc: servo-pwm: driver for controlling servo motors via PWM

This patch adds a simple driver to control servo motor position via PWM signal.
The driver allows to set the angle from userspace, while min/max positions duty cycle and the motor degrees aperture are defined in the dts.

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Driver mostly rewritten for kernel 6.2
v3:
* Fixed sysfs_emit (greg k-h)

 MAINTAINERS              |   6 ++
 drivers/misc/Kconfig     |  11 +++
 drivers/misc/Makefile    |   1 +
 drivers/misc/servo-pwm.c | 149 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 167 insertions(+)
 create mode 100644 drivers/misc/servo-pwm.c
MAINTAINERS +6 -0
index 39ff1a717625..8f4af64deb1b 100644
@@ -8737,6 +8737,12 @@ F:	Documentation/devicetree/bindings/power/power?domain*
 F:	drivers/base/power/domain*.c
 F:	include/linux/pm_domain.h
 
+GENERIC PWM SERVO DRIVER
+M:	"Angelo Compagnucci" <[email protected]>
+L:	[email protected]
+S:	Maintained
+F:	drivers/misc/servo-pwm.c
+
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
 M:	Eugen Hristev <[email protected]>
 L:	[email protected]
drivers/misc/Kconfig +11 -0
index 9947b7892bd5..8a74087149ac 100644
@@ -518,6 +518,17 @@ config VCPU_STALL_DETECTOR
 
 	  If you do not intend to run this kernel as a guest, say N.
 
+config SERVO_PWM
+	tristate "Servo motor positioning"
+	depends on PWM
+	help
+	  Driver to control generic servo motor positioning.
+	  Writing to the "angle" device attribute, the motor will move to
+	  the angle position.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called servo-pwm.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"
drivers/misc/Makefile +1 -0
index 87b54a4a4422..936629b648a9 100644
@@ -64,3 +64,4 @@ obj-$(CONFIG_HI6421V600_IRQ)	+= hi6421v600-irq.o
 obj-$(CONFIG_OPEN_DICE)		+= open-dice.o
 obj-$(CONFIG_GP_PCI1XXXX)	+= mchp_pci1xxxx/
 obj-$(CONFIG_VCPU_STALL_DETECTOR)	+= vcpu_stall_detector.o
+obj-$(CONFIG_SERVO_PWM)	+= servo-pwm.o
drivers/misc/servo-pwm.c new file +149 -0

149 lines not on this page · raw message

Signature · 1 line
2.34.1
author
#1 lore raw

PATCH v3 2/3 misc: servo-pwm: Add sysfs entries to control motor angle

Servo motor can be moved between 0 and degrees angle.

Add 'angle' sysfs attribute:
*read*: Current motor position.
*write*: Moves the motor to the position.

Add 'degrees' sysfs attribute:
*read*: how many degrees the motor can move

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Added ABI in testing
v3:
* No changes

 .../ABI/testing/sysfs-driver-servo-pwm        | 20 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 21 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-driver-servo-pwm
Documentation/ABI/testing/sysfs-driver-servo-pwm new file +20 -0
new file mode 100644
index 000000000000..9c4d897073fa
@@ -0,0 +1,20 @@
+What:		/sys/devices/platform/servo*/angle
+Date:		Feb 2023
+Contact:	Angelo Compagnucci <[email protected]>
+Description:
+		(RW) read or write servo motor position angle.
+		Servo motor can move between 0 and max degrees angle.
+		As soon the vale is written, the motor will move to the selected
+		angle. Reading the value gives the motor position.
+Users:		any user space application which wants to move the servo
+		motor position.
+
+What:		/sys/devices/platform/servo*/degrees
+Date:		Feb 2023
+Contact:	Angelo Compagnucci <[email protected]>
+Description:
+		(RO) read the servo motor movement degrees.
+		Servo motor can move between 0 and max degrees angle.
+		Reading the value gives the motor max degrees angle supported.
+Users:		any user space application which wants to know the max degrees
+		angle motor supports.
MAINTAINERS +1 -0
index 8f4af64deb1b..356daea0861d 100644
@@ -8741,6 +8741,7 @@ GENERIC PWM SERVO DRIVER
 M:	"Angelo Compagnucci" <[email protected]>
 L:	[email protected]
 S:	Maintained
+F:	Documentation/ABI/testing/sysfs-driver-servo-pwm
 F:	drivers/misc/servo-pwm.c
 
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
Signature · 1 line
2.34.1
author
#2 lore raw

PATCH v3 3/3 dt-bindings: misc: servo-pwm: Add new bindings for servo-pwm

In reply to Angelo Compagnucci

This binding describes the binding for controlling servo motors through pwm.

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Converted old txt to yaml
v3:
* Fixed errors rised by make dt_binding_check

 .../devicetree/bindings/misc/servo-pwm.yaml   | 57 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 58 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/misc/servo-pwm.yaml
Documentation/devicetree/bindings/misc/servo-pwm.yaml new file +57 -0
new file mode 100644
index 000000000000..73e81b939daf
@@ -0,0 +1,57 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/misc/servo-pwm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Servo motor connected to PWM
+
+maintainers:
+  - Angelo Compagnucci <[email protected]>
+
+description:
+  Each servo is represented as a servo-pwm device.
+  The 20ms period is the accepted standard and so most of the motors
+  support it, while the positioning min/max duty cycle or the motor
+  degrees aperture vary lot between manufacturers.
+  The most common type of servo (SG90) has 180 degrees of movement
+  and moves between 0.5ms and 2.5ms duty cycle.
+
+properties:
+  compatible:
+    const: servo-pwm
+
+  pwms:
+    maxItems: 1
+
+  pwm-names: true
+
+  degrees:
+    description:
+      How many degrees the motor can move.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
+  duty-min:
+    description:
+      Duty cycle for position the motor at 0 degrees.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
+  duty-max:
+    description:
+      Duty cycle for positioning the motor at "degrees" angle.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
+additionalProperties: false
+
+examples:
+  - |
+
+    servo: servo@0 {
+      compatible = "servo-pwm";
+      pwms = <&pwm 0 20000000 0>;
+      degrees = <180>;
+      duty-min = <500000>;
+      duty-max = <2500000>;
+    };
+
+...
MAINTAINERS +1 -0
index 356daea0861d..8f41daee62fc 100644
@@ -8742,6 +8742,7 @@ M:	"Angelo Compagnucci" <[email protected]>
 L:	[email protected]
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-driver-servo-pwm
+F:	Documentation/devicetree/bindings/misc/servo-pwm.yaml
 F:	drivers/misc/servo-pwm.c
 
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
Signature · 1 line
2.34.1
maintainer
#3 lore raw

Re: [PATCH v3 3/3] dt-bindings: misc: servo-pwm: Add new bindings for servo-pwm

Quoted 10 lines · Angelo Compagnucci

This binding describes the binding for controlling servo motors through pwm.

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Converted old txt to yaml
v3:
* Fixed errors rised by make dt_binding_check

Quoted 5 lines
 .../devicetree/bindings/misc/servo-pwm.yaml   | 57 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 58 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/misc/servo-pwm.yaml

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check' on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Documentation/devicetree/bindings/misc/servo-pwm.example.dts:19.24-25.11: Warning (unit_address_vs_reg): /example-0/servo@0: node has a unit name, but no reg or ranges property

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/[email protected]

The base for the series is generally the latest rc1. A different dependency should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above error(s), then make sure 'yamllint' is installed and dt-schema is up to date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note that DT_SCHEMA_FILES can be set to your schema file to speed up checking your schema. However, it must be unset to test all examples with your schema.

#4 lore raw

Re: [PATCH v3 3/3] dt-bindings: misc: servo-pwm: Add new bindings for servo-pwm

In reply to Angelo Compagnucci
Quoted 9 lines · Angelo Compagnucci

This binding describes the binding for controlling servo motors through pwm.

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Converted old txt to yaml
v3:
* Fixed errors rised by make dt_binding_check

Still fails the tests.

Does not look like you tested the bindings. Please run make dt_binding_check (see Documentation/devicetree/bindings/writing-schema.rst for instructions).

Quoted 29 lines
 .../devicetree/bindings/misc/servo-pwm.yaml   | 57 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 58 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/misc/servo-pwm.yaml
Documentation/devicetree/bindings/misc/servo-pwm.yaml new file +17 -0
new file mode 100644
index 000000000000..73e81b939daf
@@ -0,0 +1,57 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/misc/servo-pwm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Servo motor connected to PWM
+
+maintainers:
+  - Angelo Compagnucci <[email protected]>
+
+description:
+  Each servo is represented as a servo-pwm device.
+  The 20ms period is the accepted standard and so most of the motors
+  support it, while the positioning min/max duty cycle or the motor
+  degrees aperture vary lot between manufacturers.
+  The most common type of servo (SG90) has 180 degrees of movement

Documentation/devicetree/bindings/misc/servo-pwm.yaml line 27

Quoted 10 lines
Documentation/devicetree/bindings/misc/servo-pwm.yaml new file +10 -0
+  and moves between 0.5ms and 2.5ms duty cycle.
+
+properties:
+  compatible:
+    const: servo-pwm
+
+  pwms:
+    maxItems: 1
+
+  pwm-names: true

You got later feedback from Rob for v2, so this needs changes.

Quoted 11 lines
Documentation/devicetree/bindings/misc/servo-pwm.yaml new file +11 -0
+
+  degrees:
+    description:
+      How many degrees the motor can move.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
+  duty-min:
+    description:
+      Duty cycle for position the motor at 0 degrees.
+    $ref: /schemas/types.yaml#/definitions/uint32
+

Documentation/devicetree/bindings/misc/servo-pwm.yaml line 48

Quoted 10 lines
Documentation/devicetree/bindings/misc/servo-pwm.yaml new file +10 -0
+  duty-max:
+    description:
+      Duty cycle for positioning the motor at "degrees" angle.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
+additionalProperties: false
+
+examples:
+  - |
+

Drop blank line.

Krzysztof

build bot
#5 lore raw
In reply to Angelo Compagnucci
I love your patch! Perhaps something to improve:

Hi Angelo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on char-misc/char-misc-linus]
[also build test WARNING on linus/master v6.2-rc8]
[cannot apply to char-misc/char-misc-testing char-misc/char-misc-next next-20230217] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Angelo-Compagnucci/misc-servo-pwm-Add-sysfs-entries-to-control-motor-angle/20230218-001254
patch link:    https://lore.kernel.org/r/20230217161038.3130053-1-angelo%40amarulasolutions.com
patch subject: [PATCH v3 1/3] misc: servo-pwm: driver for controlling servo motors via PWM
config: loongarch-allyesconfig (https://download.01.org/0day-ci/archive/20230218/[email protected]/config)
compiler: loongarch64-linux-gcc (GCC) 12.1.0

reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/0ae16e16da0aa94de0d3ae63166f50a4a6fdef8a
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Angelo-Compagnucci/misc-servo-pwm-Add-sysfs-entries-to-control-motor-angle/20230218-001254 git checkout 0ae16e16da0aa94de0d3ae63166f50a4a6fdef8a
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch olddefconfig COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch SHELL=/bin/bash drivers/misc/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
| Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All warnings (new ones prefixed by >>):

In file included from include/linux/mm_types_task.h:16,
from include/linux/mm_types.h:5, from include/linux/buildid.h:5, from include/linux/module.h:14, from drivers/misc/servo-pwm.c:7:
drivers/misc/servo-pwm.c: In function 'angle_show':

>> arch/loongarch/include/asm/page.h:23:25: warning: passing argument 2 of 'sysfs_emit' makes pointer from integer without a cast [-Wint-conversion]
      23 | #define PAGE_SIZE       (_AC(1, UL) << PAGE_SHIFT)
         |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~
         |                         |
         |                         long unsigned int
   drivers/misc/servo-pwm.c:54:32: note: in expansion of macro 'PAGE_SIZE'
      54 |         return sysfs_emit(buf, PAGE_SIZE, "%u\n", data->angle);
         |                                ^~~~~~~~~
   In file included from include/linux/kobject.h:20,
                    from include/linux/module.h:21:
   include/linux/sysfs.h:357:39: note: expected 'const char *' but argument is of type 'long unsigned int'
     357 | int sysfs_emit(char *buf, const char *fmt, ...);
         |                           ~~~~~~~~~~~~^~~
   drivers/misc/servo-pwm.c: In function 'degrees_show':
>> arch/loongarch/include/asm/page.h:23:25: warning: passing argument 2 of 'sysfs_emit' makes pointer from integer without a cast [-Wint-conversion]
      23 | #define PAGE_SIZE       (_AC(1, UL) << PAGE_SHIFT)
         |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~
         |                         |
         |                         long unsigned int
   drivers/misc/servo-pwm.c:84:32: note: in expansion of macro 'PAGE_SIZE'
      84 |         return sysfs_emit(buf, PAGE_SIZE, "%u\n", data->degrees);
         |                                ^~~~~~~~~
   include/linux/sysfs.h:357:39: note: expected 'const char *' but argument is of type 'long unsigned int'
     357 | int sysfs_emit(char *buf, const char *fmt, ...);
         |                           ~~~~~~~~~~~~^~~

vim +/sysfs_emit +23 arch/loongarch/include/asm/page.h

09cfefb7fa70c3 Huacai Chen 2022-05-31  10  
09cfefb7fa70c3 Huacai Chen 2022-05-31  11  /*
09cfefb7fa70c3 Huacai Chen 2022-05-31  12   * PAGE_SHIFT determines the page size
09cfefb7fa70c3 Huacai Chen 2022-05-31  13   */
09cfefb7fa70c3 Huacai Chen 2022-05-31  14  #ifdef CONFIG_PAGE_SIZE_4KB
09cfefb7fa70c3 Huacai Chen 2022-05-31  15  #define PAGE_SHIFT	12
09cfefb7fa70c3 Huacai Chen 2022-05-31  16  #endif
09cfefb7fa70c3 Huacai Chen 2022-05-31  17  #ifdef CONFIG_PAGE_SIZE_16KB
09cfefb7fa70c3 Huacai Chen 2022-05-31  18  #define PAGE_SHIFT	14
09cfefb7fa70c3 Huacai Chen 2022-05-31  19  #endif
09cfefb7fa70c3 Huacai Chen 2022-05-31  20  #ifdef CONFIG_PAGE_SIZE_64KB
09cfefb7fa70c3 Huacai Chen 2022-05-31  21  #define PAGE_SHIFT	16
09cfefb7fa70c3 Huacai Chen 2022-05-31  22  #endif

09cfefb7fa70c3 Huacai Chen 2022-05-31 @23 #define PAGE_SIZE (_AC(1, UL) << PAGE_SHIFT)
09cfefb7fa70c3 Huacai Chen 2022-05-31 24 #define PAGE_MASK (~(PAGE_SIZE - 1))
09cfefb7fa70c3 Huacai Chen 2022-05-31 25

Signature · 2 lines
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests
build bot
#6 lore raw
In reply to Angelo Compagnucci
I love your patch! Perhaps something to improve:

Hi Angelo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on char-misc/char-misc-linus]
[also build test WARNING on linus/master v6.2-rc8]
[cannot apply to char-misc/char-misc-testing char-misc/char-misc-next next-20230217] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Angelo-Compagnucci/misc-servo-pwm-Add-sysfs-entries-to-control-motor-angle/20230218-001254
patch link:    https://lore.kernel.org/r/20230217161038.3130053-1-angelo%40amarulasolutions.com
patch subject: [PATCH v3 1/3] misc: servo-pwm: driver for controlling servo motors via PWM
config: sparc-allyesconfig (https://download.01.org/0day-ci/archive/20230218/[email protected]/config)
compiler: sparc64-linux-gcc (GCC) 12.1.0

reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/0ae16e16da0aa94de0d3ae63166f50a4a6fdef8a
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Angelo-Compagnucci/misc-servo-pwm-Add-sysfs-entries-to-control-motor-angle/20230218-001254 git checkout 0ae16e16da0aa94de0d3ae63166f50a4a6fdef8a
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=sparc olddefconfig COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=sparc SHELL=/bin/bash drivers/misc/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
| Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All warnings (new ones prefixed by >>):

In file included from arch/sparc/include/asm/page.h:8,
from arch/sparc/include/asm/sparsemem.h:7, from include/linux/numa.h:25, from include/linux/cpumask.h:16, from include/linux/mm_types_task.h:14, from include/linux/mm_types.h:5, from include/linux/buildid.h:5, from include/linux/module.h:14, from drivers/misc/servo-pwm.c:7:
drivers/misc/servo-pwm.c: In function 'angle_show':

>> arch/sparc/include/asm/page_64.h:9:22: warning: passing argument 2 of 'sysfs_emit' makes pointer from integer without a cast [-Wint-conversion]
       9 | #define PAGE_SIZE    (_AC(1,UL) << PAGE_SHIFT)
         |                      ^~~~~~~~~~~~~~~~~~~~~~~~~
         |                      |
         |                      long unsigned int
   drivers/misc/servo-pwm.c:54:32: note: in expansion of macro 'PAGE_SIZE'
      54 |         return sysfs_emit(buf, PAGE_SIZE, "%u\n", data->angle);
         |                                ^~~~~~~~~
   In file included from include/linux/kobject.h:20,
                    from include/linux/module.h:21:
   include/linux/sysfs.h:357:39: note: expected 'const char *' but argument is of type 'long unsigned int'
     357 | int sysfs_emit(char *buf, const char *fmt, ...);
         |                           ~~~~~~~~~~~~^~~
   drivers/misc/servo-pwm.c: In function 'degrees_show':
>> arch/sparc/include/asm/page_64.h:9:22: warning: passing argument 2 of 'sysfs_emit' makes pointer from integer without a cast [-Wint-conversion]
       9 | #define PAGE_SIZE    (_AC(1,UL) << PAGE_SHIFT)
         |                      ^~~~~~~~~~~~~~~~~~~~~~~~~
         |                      |
         |                      long unsigned int
   drivers/misc/servo-pwm.c:84:32: note: in expansion of macro 'PAGE_SIZE'
      84 |         return sysfs_emit(buf, PAGE_SIZE, "%u\n", data->degrees);
         |                                ^~~~~~~~~
   include/linux/sysfs.h:357:39: note: expected 'const char *' but argument is of type 'long unsigned int'
     357 | int sysfs_emit(char *buf, const char *fmt, ...);
         |                           ~~~~~~~~~~~~^~~

vim +/sysfs_emit +9 arch/sparc/include/asm/page_64.h

f5e706ad886b6a include/asm-sparc/page_64.h Sam Ravnborg 2008-07-17 8

f5e706ad886b6a include/asm-sparc/page_64.h Sam Ravnborg 2008-07-17  @9  #define PAGE_SIZE    (_AC(1,UL) << PAGE_SHIFT)
f5e706ad886b6a include/asm-sparc/page_64.h Sam Ravnborg 2008-07-17  10  #define PAGE_MASK    (~(PAGE_SIZE-1))
f5e706ad886b6a include/asm-sparc/page_64.h Sam Ravnborg 2008-07-17  11
Signature · 2 lines
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests
#7 lore raw
In reply to Angelo Compagnucci
Quoted 96 lines · Angelo Compagnucci

This patch adds a simple driver to control servo motor position via PWM signal.
The driver allows to set the angle from userspace, while min/max positions duty cycle and the motor degrees aperture are defined in the dts.

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Driver mostly rewritten for kernel 6.2
v3:
* Fixed sysfs_emit (greg k-h)

 MAINTAINERS              |   6 ++
 drivers/misc/Kconfig     |  11 +++
 drivers/misc/Makefile    |   1 +
 drivers/misc/servo-pwm.c | 149 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 167 insertions(+)
 create mode 100644 drivers/misc/servo-pwm.c
MAINTAINERS +6 -0
index 39ff1a717625..8f4af64deb1b 100644
@@ -8737,6 +8737,12 @@ F:	Documentation/devicetree/bindings/power/power?domain*
 F:	drivers/base/power/domain*.c
 F:	include/linux/pm_domain.h
 
+GENERIC PWM SERVO DRIVER
+M:	"Angelo Compagnucci" <[email protected]>
+L:	[email protected]
+S:	Maintained
+F:	drivers/misc/servo-pwm.c
+
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
 M:	Eugen Hristev <[email protected]>
 L:	[email protected]
drivers/misc/Kconfig +11 -0
index 9947b7892bd5..8a74087149ac 100644
@@ -518,6 +518,17 @@ config VCPU_STALL_DETECTOR
 
 	  If you do not intend to run this kernel as a guest, say N.
 
+config SERVO_PWM
+	tristate "Servo motor positioning"
+	depends on PWM
+	help
+	  Driver to control generic servo motor positioning.
+	  Writing to the "angle" device attribute, the motor will move to
+	  the angle position.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called servo-pwm.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"
drivers/misc/Makefile +1 -0
index 87b54a4a4422..936629b648a9 100644
@@ -64,3 +64,4 @@ obj-$(CONFIG_HI6421V600_IRQ)	+= hi6421v600-irq.o
 obj-$(CONFIG_OPEN_DICE)		+= open-dice.o
 obj-$(CONFIG_GP_PCI1XXXX)	+= mchp_pci1xxxx/
 obj-$(CONFIG_VCPU_STALL_DETECTOR)	+= vcpu_stall_detector.o
+obj-$(CONFIG_SERVO_PWM)	+= servo-pwm.o
drivers/misc/servo-pwm.c new file +22 -0
new file mode 100644
index 000000000000..1303ddda8d07
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2023 Angelo Compagnucci <[email protected]>
+ * servo-pwm.c - driver for controlling servo motors via pwm.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/err.h>
+#include <linux/pwm.h>
+
+#define DEFAULT_DUTY_MIN	500000
+#define DEFAULT_DUTY_MAX	2500000
+#define DEFAULT_DEGREES		175
+#define DEFAULT_ANGLE		0
+
+struct servo_pwm_data {
+	u32 duty_min;
+	u32 duty_max;
+	u32 degrees;
+	u32 angle;

drivers/misc/servo-pwm.c line 32

Quoted 10 lines
drivers/misc/servo-pwm.c new file +10 -0
+
+	struct mutex lock;
+	struct pwm_device *pwm;
+	struct pwm_state pwmstate;
+};
+
+static int servo_pwm_set(struct servo_pwm_data *data, int val)
+{
+	u64 new_duty = (((data->duty_max - data->duty_min) /
+			data->degrees) * val) + data->duty_min;

This one formula is basically the only thing that this driver adds. The remaining 150+ lines are essentially boilerplate to expose the "angle" property via sysfs.

We can already do everything that this driver does via the PWM sysfs, so I wonder if we really need this.

Also, how are other aspects of the motor (such as velocity) controlled? Wouldn't you want to expose these other controls as well?

Thierry

#8 lore raw
Quoted 113 lines · Thierry Reding
Quoted 96 lines · Angelo Compagnucci

This patch adds a simple driver to control servo motor position via PWM signal.
The driver allows to set the angle from userspace, while min/max positions duty cycle and the motor degrees aperture are defined in the dts.

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Driver mostly rewritten for kernel 6.2
v3:
* Fixed sysfs_emit (greg k-h)

 MAINTAINERS              |   6 ++
 drivers/misc/Kconfig     |  11 +++
 drivers/misc/Makefile    |   1 +
 drivers/misc/servo-pwm.c | 149 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 167 insertions(+)
 create mode 100644 drivers/misc/servo-pwm.c
MAINTAINERS +6 -0
index 39ff1a717625..8f4af64deb1b 100644
@@ -8737,6 +8737,12 @@ F:     Documentation/devicetree/bindings/power/power?domain*
 F:   drivers/base/power/domain*.c
 F:   include/linux/pm_domain.h
 
+GENERIC PWM SERVO DRIVER
+M:   "Angelo Compagnucci" <[email protected]>
+L:   [email protected]
+S:   Maintained
+F:   drivers/misc/servo-pwm.c
+
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
 M:   Eugen Hristev <[email protected]>
 L:   [email protected]
drivers/misc/Kconfig +11 -0
index 9947b7892bd5..8a74087149ac 100644
@@ -518,6 +518,17 @@ config VCPU_STALL_DETECTOR
 
        If you do not intend to run this kernel as a guest, say N.
 
+config SERVO_PWM
+     tristate "Servo motor positioning"
+     depends on PWM
+     help
+       Driver to control generic servo motor positioning.
+       Writing to the "angle" device attribute, the motor will move to
+       the angle position.
+
+       To compile this driver as a module, choose M here: the module
+       will be called servo-pwm.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"
drivers/misc/Makefile +1 -0
index 87b54a4a4422..936629b648a9 100644
@@ -64,3 +64,4 @@ obj-$(CONFIG_HI6421V600_IRQ)        += hi6421v600-irq.o
 obj-$(CONFIG_OPEN_DICE)              += open-dice.o
 obj-$(CONFIG_GP_PCI1XXXX)    += mchp_pci1xxxx/
 obj-$(CONFIG_VCPU_STALL_DETECTOR)    += vcpu_stall_detector.o
+obj-$(CONFIG_SERVO_PWM)      += servo-pwm.o
drivers/misc/servo-pwm.c new file +22 -0
new file mode 100644
index 000000000000..1303ddda8d07
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2023 Angelo Compagnucci <[email protected]>
+ * servo-pwm.c - driver for controlling servo motors via pwm.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/err.h>
+#include <linux/pwm.h>
+
+#define DEFAULT_DUTY_MIN     500000
+#define DEFAULT_DUTY_MAX     2500000
+#define DEFAULT_DEGREES              175
+#define DEFAULT_ANGLE                0
+
+struct servo_pwm_data {
+     u32 duty_min;
+     u32 duty_max;
+     u32 degrees;
+     u32 angle;

drivers/misc/servo-pwm.c line 32

Quoted 10 lines
drivers/misc/servo-pwm.c new file +10 -0
+
+     struct mutex lock;
+     struct pwm_device *pwm;
+     struct pwm_state pwmstate;
+};
+
+static int servo_pwm_set(struct servo_pwm_data *data, int val)
+{
+     u64 new_duty = (((data->duty_max - data->duty_min) /
+                     data->degrees) * val) + data->duty_min;

This one formula is basically the only thing that this driver adds. The remaining 150+ lines are essentially boilerplate to expose the "angle" property via sysfs.

Quoted 2 lines

We can already do everything that this driver does via the PWM sysfs, so I wonder if we really need this.

That's true, but anyway it's a big improvement over writing each one of the servo parameters inside the sysfs one by one.
Moreover, it makes easier to handle a product based on several servo motors.

Quoted 2 lines

Also, how are other aspects of the motor (such as velocity) controlled? Wouldn't you want to expose these other controls as well?

As far as I can tell, a basic servo motor only offers a way to change the angle through PWM duty cycle.
The speed is controlled by the driver inside the motor: the bigger is the angle, the faster it moves.

There are more complex servos out there, but they don't use plain simple PWM like those, they usually use some sort of more complex digital protocol on busses like I2C, SPI, DMX.

Quoted 2 lines

Thierry

Signature · 16 lines
Angelo Compagnucci

Software Engineer

[email protected]
__________________________________
Amarula Solutions SRL

Via le Canevare 30, 31100 Treviso, Veneto, IT

T. +39 (0)42 243 5310
[email protected]

www.amarulasolutions.com

[`as] https://www.amarulasolutions.com|
#9 lore raw
In reply to Angelo Compagnucci
Quoted 96 lines · Angelo Compagnucci

This patch adds a simple driver to control servo motor position via PWM signal.
The driver allows to set the angle from userspace, while min/max positions duty cycle and the motor degrees aperture are defined in the dts.

Signed-off-by Angelo Compagnucci <[email protected]>

---
v2:
* Driver mostly rewritten for kernel 6.2
v3:
* Fixed sysfs_emit (greg k-h)

 MAINTAINERS              |   6 ++
 drivers/misc/Kconfig     |  11 +++
 drivers/misc/Makefile    |   1 +
 drivers/misc/servo-pwm.c | 149 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 167 insertions(+)
 create mode 100644 drivers/misc/servo-pwm.c
MAINTAINERS +6 -0
index 39ff1a717625..8f4af64deb1b 100644
@@ -8737,6 +8737,12 @@ F:	Documentation/devicetree/bindings/power/power?domain*
 F:	drivers/base/power/domain*.c
 F:	include/linux/pm_domain.h
 
+GENERIC PWM SERVO DRIVER
+M:	"Angelo Compagnucci" <[email protected]>
+L:	[email protected]
+S:	Maintained
+F:	drivers/misc/servo-pwm.c
+
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
 M:	Eugen Hristev <[email protected]>
 L:	[email protected]
drivers/misc/Kconfig +11 -0
index 9947b7892bd5..8a74087149ac 100644
@@ -518,6 +518,17 @@ config VCPU_STALL_DETECTOR
 
 	  If you do not intend to run this kernel as a guest, say N.
 
+config SERVO_PWM
+	tristate "Servo motor positioning"
+	depends on PWM
+	help
+	  Driver to control generic servo motor positioning.
+	  Writing to the "angle" device attribute, the motor will move to
+	  the angle position.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called servo-pwm.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"
drivers/misc/Makefile +1 -0
index 87b54a4a4422..936629b648a9 100644
@@ -64,3 +64,4 @@ obj-$(CONFIG_HI6421V600_IRQ)	+= hi6421v600-irq.o
 obj-$(CONFIG_OPEN_DICE)		+= open-dice.o
 obj-$(CONFIG_GP_PCI1XXXX)	+= mchp_pci1xxxx/
 obj-$(CONFIG_VCPU_STALL_DETECTOR)	+= vcpu_stall_detector.o
+obj-$(CONFIG_SERVO_PWM)	+= servo-pwm.o
drivers/misc/servo-pwm.c new file +22 -0
new file mode 100644
index 000000000000..1303ddda8d07
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2023 Angelo Compagnucci <[email protected]>
+ * servo-pwm.c - driver for controlling servo motors via pwm.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/err.h>
+#include <linux/pwm.h>
+
+#define DEFAULT_DUTY_MIN	500000
+#define DEFAULT_DUTY_MAX	2500000
+#define DEFAULT_DEGREES		175
+#define DEFAULT_ANGLE		0
+
+struct servo_pwm_data {
+	u32 duty_min;
+	u32 duty_max;
+	u32 degrees;
+	u32 angle;

drivers/misc/servo-pwm.c line 32

Quoted 10 lines
drivers/misc/servo-pwm.c new file +10 -0
+
+	struct mutex lock;
+	struct pwm_device *pwm;
+	struct pwm_state pwmstate;
+};
+
+static int servo_pwm_set(struct servo_pwm_data *data, int val)
+{
+	u64 new_duty = (((data->duty_max - data->duty_min) /
+			data->degrees) * val) + data->duty_min;

You're loosing precision here. Always divide as late as possible. (If you need an example: With

	duty_max = 1000
	duty_min = 0
	degrees = 251
	val = 79

the exact result for new_duty would be 314.7410358565737. Your term yields 237. If you divide after multiplying with val you get 314.

All in all I think this driver is too specialized on a single motor type. IMHO what we would be more helpful is a generic framework that can abstract various different motors with the same API.

A while back I already thought about a suitable driver API. The abstraction I came up with back then was:

.setspeed(struct motor_device *motor, signed int speed) .disable(struct motor_device *motor)

In the end this is probably too simple because it doesn't allow the consumer to specify how fast the new target speed is to be reached. (Consider the motor running at 1000 and .setspeed(mymotor, 0) is called. Should this mean "actively brake", or "stop driving and just coast down"? I don't have a good idea yet that is both simple enough and still expressive that it's both useful to consumers and sensible to implement for different motor types.

Best regards
Uwe

Signature · 2 lines
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |