serial: nulldev: Add nulldev serial driver
PATCH v2 1/1 serial: nulldev: Add nulldev serial driver
From: Keng Soon Cheah <[email protected]>
Some device the serial console's initialization cannot run early during the boot process. Hence, nulldev serial device is helpful on that situation.
For example, if the serial module was implemented in FPGA. Serial initialization is prohibited to run until the FPGA was programmed.
This commit is to adding nulldev serial driver. This will allows the default console to be specified as a nulldev.
--- drivers/serial/Kconfig | 7 ++++++ drivers/serial/Makefile | 1 + drivers/serial/serial_nulldev.c | 48 +++++++++++++++++++++++++++++++++++++++++ 3 files changed, 56 insertions(+) create mode 100644 drivers/serial/serial_nulldev.c
drivers/serial/Kconfig +7 -0
@@ -409,6 +409,13 @@ config MXC_UART If you have a machine based on a Motorola IMX CPU you can enable its onboard serial port by enabling this option. +config NULLDEV_SERIAL + bool "Null serial device" + help + Select this to enable null serial device support. A null serial + device merely acts as a placeholder for a serial device and does + nothing for all it's operation. + config PIC32_SERIAL bool "Support for Microchip PIC32 on-chip UART" depends on DM_SERIAL && MACH_PIC32
drivers/serial/Makefile +1 -0
@@ -49,6 +49,7 @@ obj-$(CONFIG_BCM283X_MU_SERIAL) += serial_bcm283x_mu.o obj-$(CONFIG_MSM_SERIAL) += serial_msm.o obj-$(CONFIG_MVEBU_A3700_UART) += serial_mvebu_a3700.o obj-$(CONFIG_MPC8XX_CONS) += serial_mpc8xx.o +obj-$(CONFIG_NULLDEV_SERIAL) += serial_nulldev.o ifndef CONFIG_SPL_BUILD obj-$(CONFIG_USB_TTY) += usbtty.o
drivers/serial/serial_nulldev.c new file +48 -0
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Signature · 1 line
2.7.4
PATCH v2 1/1 serial: nulldev: Add nulldev serial driver
Hi Wilson,
Quoted 9 lines · Wilson Lee
From: Keng Soon Cheah <[email protected]>
Some device the serial console's initialization cannot run early during the boot process. Hence, nulldev serial device is helpful on that situation.
For example, if the serial module was implemented in FPGA. Serial initialization is prohibited to run until the FPGA was programmed.
I still don't fully understand this. Shouldn't the FPGA serial driver has some sort of register bits that determine if it's ready? And if not ready, the FPGA serial driver can do nothing like your null serial driver does?
Quoted 6 lines
This commit is to adding nulldev serial driver. This will allows the default console to be specified as a nulldev.
Signed-off-by Joe Hershberger <[email protected]>Signed-off-by Keng Soon Cheah <[email protected]>Cc Chen Yee Chew <[email protected]>
Quoted 7 lines
--- drivers/serial/Kconfig | 7 ++++++ drivers/serial/Makefile | 1 + drivers/serial/serial_nulldev.c | 48 +++++++++++++++++++++++++++++++++++++++++ 3 files changed, 56 insertions(+) create mode 100644 drivers/serial/serial_nulldev.c
[snip]
Regards,
Bin
PATCH v2 1/1 serial: nulldev: Add nulldev serial driver
Hi Bin Meng,
Quoted 12 lines · Bin Meng
Hi Wilson,
Quoted 8 lines · Wilson Lee
From: Keng Soon Cheah <[email protected]>
Some device the serial console's initialization cannot run early during
the boot process. Hence, nulldev serial device is helpful on that situation.
Quoted 9 lines
Quoted 3 lines
For example, if the serial module was implemented in FPGA. Serial initialization is prohibited to run until the FPGA was programmed.
I still don't fully understand this. Shouldn't the FPGA serial driver has some sort of register bits that determine if it's ready? And if not ready, the FPGA serial driver can do nothing like your null serial
driver does?
In most case we will not implement new FPGA serial driver. For example, we will try to implement the ns16550 serial module in FPGA and reuse the ns16550 driver that already exist in u-boot. The ns16550 driver will not know when is the right time to initialize the console hence causing system halt.
This nulldev console will eventually help to prevent such situation. Before the FPGA is ready, all the console initialization and output will be redirect to this nulldev console. After the FPGA is ready, "user" have the "flexibility" redirect the console to ns16550 serial module in FPGA.
Quoted 16 lines
Quoted 8 lines
This commit is to adding nulldev serial driver. This will allows the
default console to be specified as a nulldev.Signed-off-by Joe Hershberger <[email protected]>Signed-off-by Keng Soon Cheah <[email protected]>Cc Chen Yee Chew <[email protected]>Quoted 8 lines
---
drivers/serial/Kconfig | 7 ++++++
drivers/serial/Makefile | 1 +
drivers/serial/serial_nulldev.c | 48
+++++++++++++++++++++++++++++++++++++++++3 files changed, 56 insertions(+)create mode 100644
drivers/serial/serial_nulldev.c
Quoted 4 lines
[snip]
Regards,
Bin
Thanks.
Best Regards,
Wilson Lee
PATCH v2 1/1 serial: nulldev: Add nulldev serial driver
In reply to Wilson LeeQuoted 9 lines · Wilson Lee
From: Keng Soon Cheah <[email protected]>
Some device the serial console's initialization cannot run early during the boot process. Hence, nulldev serial device is helpful on that situation.
For example, if the serial module was implemented in FPGA. Serial initialization is prohibited to run until the FPGA was programmed.
Quoted 6 lines
This commit is to adding nulldev serial driver. This will allows the default console to be specified as a nulldev.
Signed-off-by Joe Hershberger <[email protected]>Signed-off-by Keng Soon Cheah <[email protected]>Cc Chen Yee Chew <[email protected]>
Applied to u-boot/master, thanks!
Signature · 8 lines
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