Re: [PATCH 2/2] pwm: Add support for Xilinx AXI Timer

[Sean Anderson]

On 5/4/21 8:32 AM, Michal Simek wrote:
>
>
> On 5/4/21 10:51 AM, Uwe Kleine-König wrote:
>> Hello,
>>
>> On Mon, May 03, 2021 at 05:44:13PM -0400, Sean Anderson wrote:
>>> This adds PWM support for Xilinx LogiCORE IP AXI soft timers commonly
>>> found on Xilinx FPGAs. There is another driver for this device located
>>> at arch/microblaze/kernel/timer.c, but it is only used for timekeeping.
>>> This driver was written with reference to Xilinx DS764 for v1.03.a [1].
>>>
>>> [1] https://www.xilinx.com/support/documentation/ip_documentation/axi_timer/v1_03_a/axi_timer_ds764.pdf
>>>
>>> Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxx>
>>> ---
>>>
>>>   arch/arm64/configs/defconfig |   1 +
>>>   drivers/pwm/Kconfig          |  11 ++
>>>   drivers/pwm/Makefile         |   1 +
>>>   drivers/pwm/pwm-xilinx.c     | 322 +++++++++++++++++++++++++++++++++++
>>>   4 files changed, 335 insertions(+)
>>>   create mode 100644 drivers/pwm/pwm-xilinx.c
>>>
>>> diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
>>> index 08c6f769df9a..81794209f287 100644
>>> --- a/arch/arm64/configs/defconfig
>>> +++ b/arch/arm64/configs/defconfig
>>> @@ -1083,6 +1083,7 @@ CONFIG_PWM_SAMSUNG=y
>>>   CONFIG_PWM_SL28CPLD=m
>>>   CONFIG_PWM_SUN4I=m
>>>   CONFIG_PWM_TEGRA=m
>>> +CONFIG_PWM_XILINX=m
>>>   CONFIG_SL28CPLD_INTC=y
>>>   CONFIG_QCOM_PDC=y
>>>   CONFIG_RESET_IMX7=y
>>
>> I think this should go into a separate patch once this driver is
>> accepted. This can then go via the ARM people.
>>
>>> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>>> index d3371ac7b871..01e62928f4bf 100644
>>> --- a/drivers/pwm/Kconfig
>>> +++ b/drivers/pwm/Kconfig
>>> @@ -628,4 +628,15 @@ config PWM_VT8500
>>>   	  To compile this driver as a module, choose M here: the module
>>>   	  will be called pwm-vt8500.
>>>
>>> +config PWM_XILINX
>>> +	tristate "Xilinx AXI Timer PWM support"
>>> +	depends on !MICROBLAZE
>>
>> I don't understand this dependency.
>
> The dependency is clear here because microblaze has already driver for
> this timer here arch/microblaze/kernel/timer.c.
>
> And that's exactly pointing to the way how this should be done.
> IP itself is single or dual timer and in case of dual timer you can
> select if there is pwm output and use it for PWM generation.
>
> It means it is timer with PMW together.
> I didn't have a time but Uwe likely knows this better how to design it.
>
> I see that gpio-mvebu driver instantiate pwm driver. Maybe that's the
> way to go.

I think drivers/clocksource/samsung_pwm_timer.c and
drivers/pwm/pwm-samsung.c provide another example for how to go about
this.

> Step first is move axi timer driver from microblaze to generic location.

Yes. However, I don't have a microblaze setup, so I have just added the
PWM driver.

> Figured it out how to add PWM (with DT flag) and then write support for it.

I would really like to see a standard way of doing this. Many timers
also have PWM support (e.g. samsung, and also DW). I think it's unusual
that this problem has not already been addressed.

--Sean

>
> Thanks,
> Michal
>