of: Add generic device tree DMA helpers
Subsystems (3)
v4 cover of: Add generic device tree DMA helpers
This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2] to add some basic device-tree helpers to retrieve a DMA controller device_node and the DMA request/channel information.
[1] http://article.gmane.org/gmane.linux.drivers.devicetree/12022
[2] http://article.gmane.org/gmane.linux.ports.arm.omap/73622
Jon Hunter (2):
of: Add generic device tree DMA helpers
dmaengine: add helper function to request a slave DMA channel
Documentation/devicetree/bindings/dma/dma.txt | 62 +++++++ drivers/dma/dmaengine.c | 16 ++ drivers/of/Makefile | 2 +- drivers/of/dma.c | 215 +++++++++++++++++++++++++ include/linux/dmaengine.h | 6 + include/linux/of_dma.h | 45 ++++++ 6 files changed, 345 insertions(+), 1 deletion(-) create mode 100644 Documentation/devicetree/bindings/dma/dma.txt create mode 100644 drivers/of/dma.c create mode 100644 include/linux/of_dma.h
Signature · 1 line
1.7.9.5
PATCH v4 1/2 of: Add generic device tree DMA helpers
This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2] to add some basic helpers to retrieve a DMA controller device_node and the DMA request/channel information.
Aim of DMA helpers
- The purpose of device-tree is to describe the capabilites of the hardware. Thinking about DMA controllers purely from the context of the hardware to begin with, we can describe a device in terms of a DMA controller as follows ...
1. Number of DMA controllers
2. Number of channels (maybe physical or logical)
3. Mapping of DMA requests signals to DMA controller
4. Number of DMA interrupts
5. Mapping of DMA interrupts to channels
- With the above in mind the aim of the DT DMA helper functions is to extract the above information from the DT and provide to the appropriate driver. However, due to the vast number of DMA controllers and not all are using a common driver (such as DMA Engine) it has been seen that this is not a trivial task. In previous discussions on this topic the following concerns have been raised ...
1. How does the binding support devices with multiple DMA controllers?
2. How to support both legacy DMA controllers not using DMA Engine as well as those that support DMA Engine.
3. When using with DMA Engine how do we support the various implementations where the opaque filter function parameter differs between implementations?
4. How do we handle DMA channels that are identified with a string versus a integer?
- Hence the design of the DMA helpers has to accomodate the above or align on an agreement what can be or should be supported.
Design of DMA helpers
1. Registering DMA controllers
In the case of DMA controllers that are using DMA Engine, requesting a channel is performed by calling the following function.
struct dma_chan *dma_request_channel(dma_cap_mask_t mask, dma_filter_fn filter_fn, void *filter_param);
The mask variable is used to match a type of the device controller in a list of controllers. The filter_fn and filter_param are used to identify the required dma channel and return a handle to the dma channel of type dma_chan.
From the examples I have seen, the mask and filter_fn are constant for a given DMA controller and therefore, we can specify these as controller specific data when registering the DMA controller with the device-tree DMA helpers.
The filter_param variable is of an unknown type and is typically specific to the DMA engine implementation for a given DMA controller. To allow some flexibility in the type and formating of this filter_param we employ an xlate to translate the device-tree binding information into the appropriate format. The xlate function used for a DMA controller can also be specified when registering the DMA controller with the device-tree DMA helpers.
Based upon the above, a function for registering the DMA controller with the DMA helpers now looks like the below. The data variable is used to pass a pointer to DMA controller specific data used by the xlate function.
int of_dma_controller_register(struct device_node *np,
struct dma_chan *(*of_dma_xlate) (struct of_phandle_args *, struct of_dma *), void *data)
For example, in the case where DMA engine is used, we define the following structure (that stores the DMA engine capability mask and filter function) and pass this to the data variable in the above function.
struct of_dma_filter_info {
dma_cap_mask_t dma_cap;
dma_filter_fn filter_fn;
};2. Representing and requesting channel information
Please see the dma binding documentation included in this patch for a description of how DMA controllers and client information should be represented with device-tree. For more information on how this binding came about please see [3]. In addition to this, feedback received from the Linux kernel summit showed a consensus (among those who attended) to use a name to identify DMA client information [4].
A DMA channel can be requested by calling the following function, where name is a required parameter used for identifying a DMA channel. This function has been designed to return a structure of type dma_chan to work with the DMA engine driver. Note that if DMA engine is used then drivers should be using the DMA engine API dma_request_slave_channel() (implemented in part 2 of this series, "dmaengine: add helper function to request a slave DMA channel") which will in turn call the below function if device-tree is present. The aim being to have a common DMA engine interface regardless of whether device tree is being used.
struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
char *name)
3. Supporting legacy devices not using DMA Engine
These devices present a problem, as there may not be a uniform way to easily support them with regard to device tree. Ideally, these should be migrated to DMA engine. However, if this is not possible, then they should still be able to use this binding, the only constaint imposed by this implementation is that when requesting a DMA channel via of_dma_request_slave_channel(), it will return a type of dma_chan.
This implementation has been tested on OMAP4430 using the kernel v3.6-rc5. I have validated that MMC is working on the PANDA board with this implementation. My development branch for testing on OMAP can be found here [5].
v4: - revert the removal of xlate function from v3
- update the proposed binding format and APIs based upon discussions [3]
v3: - avoid passing an xlate function and instead pass DMA engine parameters
- define number of dma channels and requests in dma-controller node
v2: - remove of_dma_to_resource API
- make property #dma-cells required (no fallback anymore)
- another check in of_dma_xlate_onenumbercell() function
[1] http://article.gmane.org/gmane.linux.drivers.devicetree/12022
[2] http://article.gmane.org/gmane.linux.ports.arm.omap/73622
[3] http://marc.info/?l=linux-omap&m=133582085008539&w=2
[4] http://pad.linaro.org/arm-mini-summit-2012
[5] https://github.com/jonhunter/linux/tree/dev-dt-dma
--- Documentation/devicetree/bindings/dma/dma.txt | 62 +++++++ drivers/of/Makefile | 2 +- drivers/of/dma.c | 215 +++++++++++++++++++++++++ include/linux/of_dma.h | 45 ++++++ 4 files changed, 323 insertions(+), 1 deletion(-) create mode 100644 Documentation/devicetree/bindings/dma/dma.txt create mode 100644 drivers/of/dma.c create mode 100644 include/linux/of_dma.h
Documentation/devicetree/bindings/dma/dma.txt new file +62 -0
@@ -0,0 +1,62 @@ +* Generic DMA Controller and DMA request bindings + +Generic binding to provide a way for a driver using DMA Engine to retrieve the +DMA request or channel information that goes from a hardware device to a DMA +controller. + + +* DMA controller + +Required property: +- #dma-cells: Must be at least 1. Used to provide DMA controller + specific information. See DMA client binding below for + more details. + +Optional properties: +- #dma-channels: Number of DMA channels supported by the controller. +- #dma-requests: Number of DMA requests signals supported by the + controller. + +Example: + + sdma: dmaengine at 48000000 { + compatible = "ti,omap-sdma" + reg = <0x48000000 0x1000>; + interrupts = <0 12 0x4 + 0 13 0x4 + 0 14 0x4 + 0 15 0x4>; + #dma-cells = <1>; + #dma-channels = <32>; + #dma-requests = <127>; + }; + + +* DMA client + +Client drivers should specify the DMA property using a phandle to the controller +followed by DMA controller specific data. + +Required property: +- dmas: List of one or more DMA specifiers, each consisting of + - A phandle pointing to DMA controller node + - A single integer cell containing DMA controller + specific information. This typically contains a dma + request line number or a channel number, but can + contain any data that is used required for configuring + a channel. +- dma-names: Contains one identifier string for each dma specifier in + the dmas property. The specific strings that can be used + are defined in the binding of the DMA client device. + +Example: + +- One DMA write channel, one DMA read/write channel: + + i2c1: i2c at 1 { + ... + dmas = <&sdma 2 /* read channel */ + &sdma 3>; /* write channel */ + dma-names = "rx", "tx" + ... + };
drivers/of/Makefile +1 -1
@@ -1,4 +1,4 @@ -obj-y = base.o +obj-y = base.o dma.o obj-$(CONFIG_OF_FLATTREE) += fdt.o obj-$(CONFIG_OF_PROMTREE) += pdt.o obj-$(CONFIG_OF_ADDRESS) += address.o
drivers/of/dma.c new file +215 -0
215 lines not on this page · raw message
include/linux/of_dma.h new file +45 -0
45 lines not on this page · raw message
Signature · 1 line
1.7.9.5
PATCH v4 1/2 of: Add generic device tree DMA helpers
Quoted 3 lines · Jon Hunter
This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2] to add some basic helpers to retrieve a DMA controller
device_nodeand the DMA request/channel information.
I think we're getting very close now, I only have a few small comments left that should all be uncontroversial.
Quoted 5 lines
Documentation/devicetree/bindings/dma/dma.txt new file +5
-0+ +Client drivers should specify the DMA property using a phandle to the controller +followed by DMA controller specific data. + +Required property:
Documentation/devicetree/bindings/dma/dma.txt line 50
Quoted 10 lines
Documentation/devicetree/bindings/dma/dma.txt new file +10
-0+- dmas: List of one or more DMA specifiers, each consisting of + - A phandle pointing to DMA controller node + - A single integer cell containing DMA controller + specific information. This typically contains a dma + request line number or a channel number, but can + contain any data that is used required for configuring + a channel. +- dma-names: Contains one identifier string for each dma specifier in + the dmas property. The specific strings that can be used + are defined in the binding of the DMA client device.
I think here we need to clarify that listing the same name multiple times implies having multiple alternatives for the same channel.
Documentation/devicetree/bindings/dma/dma.txt line 62
Quoted 11 lines
Documentation/devicetree/bindings/dma/dma.txt new file +11
-0+Example: + +- One DMA write channel, one DMA read/write channel: + + i2c1: i2c at 1 { + ... + dmas = <&sdma 2 /* read channel */ + &sdma 3>; /* write channel */ + dma-names = "rx", "tx" + ... + };
And please add an example documenting this case.
Quoted 21 lines
drivers/of/dma.c new file +21
-0+/** +* of_dma_find_channel - Find a DMA channel by name +* @np: device node to look for DMA channels +* @name: name of desired channel +* @dma_spec: pointer to DMA specifier as found in the device tree +* +* Find a DMA channel by the name. Returns 0 on success or appropriate +* errno value on error. +*/ +static int of_dma_find_channel (struct device_node *np,char *name, +struct of_phandle_args *dma_spec) +{ +int count, i; +const char *s; + + count =of_property_count_strings (np,"dma-names" ); +if (count <0 ) +return count; + +for (i =0 ; i < count; i++) { +of_property_read_string_index (np,"dma-names" , i, &s);
drivers/of/dma.c line 140
Quoted 10 lines
drivers/of/dma.c new file +10
-0+ +if (strcmp (name, s)) +continue ; + +return of_parse_phandle_with_args (np,"dmas" ,"#dma-cells" , + i, dma_spec); + } + +return -ENODEV ; +}
I think we should at least keep trying the other channels with the same name when of_parse_phandle_with_args fails. We might want to do something smarter in the long run, e.g. to spread channel allocations across the avaialable controllers.
drivers/of/dma.c line 188
Quoted 13 lines
drivers/of/dma.c new file +12
-0+/** +* of_dma_request_slave_channel - Get the DMA slave channel +* @np: device node to get DMA request from +* @name: name of desired channel +* +* Returns pointer to appropriate dma channel on success or NULL on error. +*/ +struct dma_chan *of_dma_request_slave_channel (struct device_node *np, +char *name) +{ +} +EXPORT_SYMBOL_GPL (of_dma_request_slave_channel);
I think this no longer needs to be exported, with patch 2 on top.
Quoted 16 lines
drivers/of/dma.c new file +16
-0+/** +* of_dma_simple_xlate - Simple DMA engine translation function +* @dma_spec: pointer to DMA specifier as found in the device tree +* @of_dma: pointer to DMA controller data +* +* A simple translation function for devices that use a 32-bit value for the +* filter_param when calling the DMA engine dma_request_channel() function. +* Note that this translation function requires that #dma-cells is equal to 1 +* and the argument of the dma specifier is the 32-bit filter_param. Returns +* pointer to appropriate dma channel on success or NULL on error. +*/ +struct dma_chan *of_dma_simple_xlate (struct of_phandle_args *dma_spec, +struct of_dma *ofdma) +{ +int count = dma_spec->args_count; +struct of_dma_filter_info *info = ofdma->of_dma_data;
drivers/of/dma.c line 215
Quoted 10 lines
drivers/of/dma.c new file +10
-0+ +if (!info || !info->filter_fn) +return NULL ; + +if (count !=1 ) +return NULL ; + +return dma_request_channel (info->dma_cap, info->filter_fn, + &dma_spec->args[0 ]); +}
But this one does.
Arnd
PATCH v4 1/2 of: Add generic device tree DMA helpers
Hi Arnd,
Quoted 18 lines · Arnd Bergmann
Quoted 3 lines · Jon Hunter
This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2] to add some basic helpers to retrieve a DMA controller
device_nodeand the DMA request/channel information.I think we're getting very close now, I only have a few small comments left that should all be uncontroversial.
Quoted 10 lines
Documentation/devicetree/bindings/dma/dma.txt new file +10
-0+ +Client drivers should specify the DMA property using a phandle to the controller +followed by DMA controller specific data. + +Required property: +- dmas: List of one or more DMA specifiers, each consisting of + - A phandle pointing to DMA controller node + - A single integer cell containing DMA controller + specific information. This typically contains a dma + request line number or a channel number, but can
Quoted 8 lines
Documentation/devicetree/bindings/dma/dma.txt line 50
Quoted 5 lines
Documentation/devicetree/bindings/dma/dma.txt new file +5
-0+ contain any data that is used required for configuring + a channel. +- dma-names: Contains one identifier string for each dma specifier in + the dmas property. The specific strings that can be used + are defined in the binding of the DMA client device.I think here we need to clarify that listing the same name multiple times implies having multiple alternatives for the same channel.
Ok, however, the way it works right now is that we will use the first specifier that matches the name. So if there are multiple with the same name that would imply that someone will need call the xxx_request_slave_channel() multiple times to extract these. Is that ok?
Quoted 5 lines
Quoted 5 lines
Documentation/devicetree/bindings/dma/dma.txt new file +5
-0+Example: + +- One DMA write channel, one DMA read/write channel: + + i2c1: i2c at 1 {
Quoted 8 lines
Documentation/devicetree/bindings/dma/dma.txt line 62
Quoted 6 lines
Documentation/devicetree/bindings/dma/dma.txt new file +6
-0+ ... + dmas = <&sdma 2 /* read channel */ + &sdma 3>; /* write channel */ + dma-names = "rx", "tx" + ... + };And please add an example documenting this case.
Ok.
Quoted 27 lines
Quoted 27 lines
drivers/of/dma.c new file +27
-0+/** +* of_dma_find_channel - Find a DMA channel by name +* @np: device node to look for DMA channels +* @name: name of desired channel +* @dma_spec: pointer to DMA specifier as found in the device tree +* +* Find a DMA channel by the name. Returns 0 on success or appropriate +* errno value on error. +*/ +static int of_dma_find_channel (struct device_node *np,char *name, +struct of_phandle_args *dma_spec) +{ +int count, i; +const char *s; + + count =of_property_count_strings (np,"dma-names" ); +if (count <0 ) +return count; + +for (i =0 ; i < count; i++) { +of_property_read_string_index (np,"dma-names" , i, &s); + +if (strcmp (name, s)) +continue ; + +return of_parse_phandle_with_args (np,"dmas" ,"#dma-cells" , + i, dma_spec);
Quoted 8 lines
drivers/of/dma.c line 140
Quoted 4 lines
drivers/of/dma.c new file +4
-0+ } + +return -ENODEV ; +}I think we should at least keep trying the other channels with the same name when
of_parse_phandle_with_argsfails. We might want to do something smarter in the long run, e.g. to spread channel allocations across the avaialable controllers.
Ok, can add this.
Quoted 7 lines
Quoted 7 lines
+/**
+ *of_dma_request_slave_channel- Get the DMA slave channel
+ * @np: device node to get DMA request from
+ * @name: name of desired channel
+ *
+ * Returns pointer to appropriate dma channel on success or NULL on error.
+ */
Quoted 8 lines
drivers/of/dma.c line 188
Quoted 6 lines
drivers/of/dma.c new file +5
-0+struct dma_chan *of_dma_request_slave_channel (struct device_node *np, +char *name) +{ +} +EXPORT_SYMBOL_GPL (of_dma_request_slave_channel);I think this no longer needs to be exported, with patch 2 on top.
Right, I was in two minds but I can remove this.
Quoted 20 lines
Quoted 20 lines
drivers/of/dma.c new file +20
-0+/** +* of_dma_simple_xlate - Simple DMA engine translation function +* @dma_spec: pointer to DMA specifier as found in the device tree +* @of_dma: pointer to DMA controller data +* +* A simple translation function for devices that use a 32-bit value for the +* filter_param when calling the DMA engine dma_request_channel() function. +* Note that this translation function requires that #dma-cells is equal to 1 +* and the argument of the dma specifier is the 32-bit filter_param. Returns +* pointer to appropriate dma channel on success or NULL on error. +*/ +struct dma_chan *of_dma_simple_xlate (struct of_phandle_args *dma_spec, +struct of_dma *ofdma) +{ +int count = dma_spec->args_count; +struct of_dma_filter_info *info = ofdma->of_dma_data; + +if (!info || !info->filter_fn) +return NULL ; +
Quoted 8 lines
drivers/of/dma.c line 215
Quoted 6 lines
drivers/of/dma.c new file +6
-0+if (count !=1 ) +return NULL ; + +return dma_request_channel (info->dma_cap, info->filter_fn, + &dma_spec->args[0 ]); +}But this one does.
Good catch!
Thanks
Jon
PATCH v4 1/2 of: Add generic device tree DMA helpers
Quoted 20 lines · Jon Hunter
Quoted 10 lines · Arnd Bergmann
Quoted 10 lines
Documentation/devicetree/bindings/dma/dma.txt new file +10
-0+ +Client drivers should specify the DMA property using a phandle to the controller +followed by DMA controller specific data. + +Required property: +- dmas: List of one or more DMA specifiers, each consisting of + - A phandle pointing to DMA controller node + - A single integer cell containing DMA controller + specific information. This typically contains a dma + request line number or a channel number, but canQuoted 8 lines
Documentation/devicetree/bindings/dma/dma.txt line 50
Quoted 5 lines
Documentation/devicetree/bindings/dma/dma.txt new file +5
-0+ contain any data that is used required for configuring + a channel. +- dma-names: Contains one identifier string for each dma specifier in + the dmas property. The specific strings that can be used + are defined in the binding of the DMA client device.I think here we need to clarify that listing the same name multiple times implies having multiple alternatives for the same channel.
Quoted 4 lines
Ok, however, the way it works right now is that we will use the first specifier that matches the name. So if there are multiple with the same name that would imply that someone will need call the
xxx_request_slave_channel()multiple times to extract these. Is that ok?
I would expect a driver to only call the function once, and get something back from the dmaengine layer that works. If there are two controllers to choose from and one is busy, then it should definitely give a channel from the non-busy one.
It's not much of an issue if the code doesn't handle all corner cases at first, but I would expect that the binding correctly describes how to write a device tree that will work once the code implements it correctly.
Arnd
PATCH v4 1/2 of: Add generic device tree DMA helpers
Quoted 26 lines · Arnd Bergmann
Quoted 20 lines · Jon Hunter
Quoted 10 lines · Arnd Bergmann
Quoted 10 lines
(quoted diff) +10
-0+ +Client drivers should specify the DMA property using a phandle to the controller +followed by DMA controller specific data. + +Required property: +- dmas: List of one or more DMA specifiers, each consisting of + - A phandle pointing to DMA controller node + - A single integer cell containing DMA controller + specific information. This typically contains a dma + request line number or a channel number, but canQuoted 8 lines
Review
Quoted 5 lines
(quoted diff) +5
-0+ contain any data that is used required for configuring + a channel. +- dma-names: Contains one identifier string for each dma specifier in + the dmas property. The specific strings that can be used + are defined in the binding of the DMA client device.I think here we need to clarify that listing the same name multiple times implies having multiple alternatives for the same channel.
Quoted 4 lines
Ok, however, the way it works right now is that we will use the first specifier that matches the name. So if there are multiple with the same name that would imply that someone will need call the
xxx_request_slave_channel()multiple times to extract these. Is that ok?
Quoted 8 lines
I would expect a driver to only call the function once, and get something back from the dmaengine layer that works. If there are two controllers to choose from and one is busy, then it should definitely give a channel from the non-busy one.
It's not much of an issue if the code doesn't handle all corner cases at first, but I would expect that the binding correctly describes how to write a device tree that will work once the code implements it correctly.
Gotcha, may be something like the following should work then ...
drivers/of/dma.c +26 -23
@@ -127,13 +127,15 @@ static int of_dma_find_channel(struct device_node *np, char *name,return count;for (i =0 ; i < count; i++) { -of_property_read_string_index (np,"dma-names" , i, &s); +if (of_property_read_string_index (np,"dma-names" , i, &s)) +continue ;if (strcmp (name, s))continue ; -return of_parse_phandle_with_args (np,"dmas" ,"#dma-cells" , - i, dma_spec); +if (!of_parse_phandle_with_args (np,"dmas" ,"#dma-cells" , i, + dma_spec)) +return 0 ; }return -ENODEV ;
@@ -159,33 +161,34 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,return NULL ; } - r =of_dma_find_channel (np, name, &dma_spec); - -if (r) { -pr_err ("%s: can't find DMA channel\n" , np->full_name); -return NULL ; - } +do { + r =of_dma_find_channel (np, name, &dma_spec); +if (r) { +pr_err ("%s: can't find DMA channel\n" , np->full_name); +return NULL ; + } + + ofdma =of_dma_find_controller (dma_spec.np); +if (!ofdma) { +pr_debug ("%s: can't find DMA controller %s\n" , + np->full_name, dma_spec.np->full_name); +continue ; + } - ofdma =of_dma_find_controller (dma_spec.np); -if (!ofdma) { -pr_err ("%s: can't find DMA controller %s\n" , np->full_name, - dma_spec.np->full_name); -return NULL ; - } +if (dma_spec.args_count != ofdma->of_dma_nbcells) { +pr_debug ("%s: wrong #dma-cells for %s\n" , np->full_name, + dma_spec.np->full_name); +continue ; + } -if (dma_spec.args_count != ofdma->of_dma_nbcells) { -pr_err ("%s: wrong #dma-cells for %s\n" , np->full_name, - dma_spec.np->full_name); -return NULL ; - } + chan = ofdma->of_dma_xlate (&dma_spec, ofdma); - chan = ofdma->of_dma_xlate (&dma_spec, ofdma); +of_node_put (dma_spec.np); -of_node_put (dma_spec.np); + }while (!chan);return chan; } -EXPORT_SYMBOL_GPL (of_dma_request_slave_channel);
Cheers
Jon
PATCH v4 1/2 of: Add generic device tree DMA helpers
In reply to Jon HunterQuoted 18 lines · Jon Hunter
This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2] to add some basic helpers to retrieve a DMA controller
device_nodeand the DMA request/channel information.Documentation/devicetree/bindings/dma/dma.txt +12
-0+* Generic DMA Controller and DMA request bindings + +Generic binding to provide a way for a driver using DMA Engine to retrieve the +DMA request or channel information that goes from a hardware device to a DMA +controller. + + +* DMA controller + +Required property: +- #dma-cells: Must be at least 1. Used to provide DMA controller + specific information. See DMA client binding below for
...
Documentation/devicetree/bindings/dma/dma.txt line 47
Quoted 13 lines
Documentation/devicetree/bindings/dma/dma.txt +13
-0+* DMA client + +Client drivers should specify the DMA property using a phandle to the controller +followed by DMA controller specific data. + +Required property: +- dmas: List of one or more DMA specifiers, each consisting of + - A phandle pointing to DMA controller node + - A single integer cell containing DMA controller + specific information. This typically contains a dma + request line number or a channel number, but can + contain any data that is used required for configuring + a channel.
"A single integer cell" doesn't sound correct; shouldn't this be something like "a number of integer cells, as determined by the #dma-cells property in the node referenced by phandle"?
Quoted 3 lines
+- dma-names: Contains one identifier string for each dma specifier in
Documentation/devicetree/bindings/dma/dma.txt +2
-0+ the dmas property. The specific strings that can be used + are defined in the binding of the DMA client device.
PATCH v4 1/2 of: Add generic device tree DMA helpers
Quoted 29 lines · Stephen Warren
Quoted 18 lines · Jon Hunter
This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2] to add some basic helpers to retrieve a DMA controller
device_nodeand the DMA request/channel information.Documentation/devicetree/bindings/dma/dma.txt +12
-0+* Generic DMA Controller and DMA request bindings + +Generic binding to provide a way for a driver using DMA Engine to retrieve the +DMA request or channel information that goes from a hardware device to a DMA +controller. + + +* DMA controller + +Required property: +- #dma-cells: Must be at least 1. Used to provide DMA controller + specific information. See DMA client binding below for...
Quoted 9 lines
Documentation/devicetree/bindings/dma/dma.txt +9
-0+* DMA client + +Client drivers should specify the DMA property using a phandle to the controller +followed by DMA controller specific data. + +Required property: +- dmas: List of one or more DMA specifiers, each consisting of + - A phandle pointing to DMA controller node + - A single integer cell containing DMA controller
Quoted 8 lines
Documentation/devicetree/bindings/dma/dma.txt line 47
Quoted 4 lines
Documentation/devicetree/bindings/dma/dma.txt +4
-0+ specific information. This typically contains a dma + request line number or a channel number, but can + contain any data that is used required for configuring + a channel."A single integer cell" doesn't sound correct; shouldn't this be something like "a number of integer cells, as determined by the #dma-cells property in the node referenced by phandle"?
Thanks for catching that. I had been re-working this a few times and must have forgotten to update that.
Cheers
Jon
PATCH v4 2/2 dmaengine: add helper function to request a slave DMA channel
In reply to Jon HunterCurrently slave DMA channels are requested by calling dma_request_channel() and requires DMA clients to pass various filter parameters to obtain the appropriate channel.
With device-tree being used by architectures such as arm and the addition of device-tree helper functions to extract the relevant DMA client information from device-tree, add a new function to request a slave DMA channel using device-tree. This function is currently a simple wrapper that calls the device-tree of_dma_request_slave_channel() function.
--- drivers/dma/dmaengine.c | 16 ++++++++++++++++ include/linux/dmaengine.h | 6 ++++++ 2 files changed, 22 insertions(+)
drivers/dma/dmaengine.c +16 -0
@@ -62,6 +62,7 @@#include <linux/rculist.h> #include <linux/idr.h> #include <linux/slab.h> +#include <linux/of_dma.h> static DEFINE_MUTEX (dma_list_mutex);static DEFINE_IDR (dma_idr);
@@ -546,6 +547,21 @@ struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, dma_filter_fn fn, v }EXPORT_SYMBOL_GPL (__dma_request_channel); +/** +* dma_request_slave_channel - try to allocate an exclusive slave channel +* @dev: pointer to client device structure +* @name: slave channel name +*/ +struct dma_chan *dma_request_slave_channel (struct device *dev,char *name) +{ +/* If device-tree is present get slave info from here */ +if (dev->of_node) +return of_dma_request_slave_channel (dev->of_node, name); + +return NULL ; +} +EXPORT_SYMBOL_GPL (dma_request_slave_channel); +void dma_release_channel (struct dma_chan *chan) {mutex_lock (&dma_list_mutex);
include/linux/dmaengine.h +6 -0
@@ -973,6 +973,7 @@ enum dma_status dma_sync_wait(struct dma_chan *chan, dma_cookie_t cookie);enum dma_status dma_wait_for_async_tx (struct dma_async_tx_descriptor *tx);void dma_issue_pending_all (void );struct dma_chan *__dma_request_channel (dma_cap_mask_t *mask,dma_filter_fn fn,void *fn_param); +struct dma_chan *dma_request_slave_channel (struct device *dev,char *name);void dma_release_channel (struct dma_chan *chan);#else static inline enum dma_status dma_wait_for_async_tx (struct dma_async_tx_descriptor *tx)
@@ -987,6 +988,11 @@ static inline struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, {return NULL ; } +static inline struct dma_chan *dma_request_slave_channel (struct device *dev, +char *name) +{ + return NULL +}static inline void dma_release_channel (struct dma_chan *chan) { }
Signature · 1 line
1.7.9.5