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

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Date:   Tue, 4 May 2021 14:32:06 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Sean Anderson <sean.anderson@...o.com>
CC:     <linux-pwm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <michal.simek@...inx.com>,
        Lee Jones <lee.jones@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH 2/2] pwm: Add support for Xilinx AXI Timer



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@...o.com>
>> ---
>>
>>  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.

Step first is move axi timer driver from microblaze to generic location.
Figured it out how to add PWM (with DT flag) and then write support for it.

Thanks,
Michal