Re: [Linuxptp-devel] [RFC PATCH v2 2/3] pwm: Add helper apis to control pwm

[Lokesh Vutla via Linuxptp-devel]

On 19/05/20 9:16 pm, Richard Cochran wrote:
> On Tue, May 19, 2020 at 11:41:45AM +0000, Geva, Erez wrote:
>> From a quick look.
>> It seems that it is 'pwmchip%d' for a long time.
>>
>> https://elixir.bootlin.com/linux/v4.0/source/drivers/pwm/sysfs.c#L314
> 
> Looks like my v4.19.25-rt16 kernel has a bad commit with a regression.
> 
> The documentation, Documentation/ABI/testing/sysfs-class-pwm, is
> clear, and it has been that way since kernel 3.11.

Cool. Then patch need not be updated for multiple ABIs.

Thanks and regards,
Lokesh

> 
> Mainline has this:
> 
> commit c289d6625237aa785b484b4e94c23b3b91ea7e60
> Author: Fabrice Gasnier <fabrice.gasn...@st.com>
> Date:   Mon Oct 1 15:23:56 2018 +0200
> 
>     Revert "pwm: Set class for exported channels in sysfs"
>     
>     This reverts commit 7e5d1fd75c3dde9fc10c4472b9368089d1b81d00 ("pwm: Set
>     class for exported channels in sysfs") as it causes regression with
>     multiple pwm chip[1], when exporting a pwm channel (echo X > export):
>     
>     - ABI (Documentation/ABI/testing/sysfs-class-pwm) states pwmX should be
>       created in /sys/class/pwm/pwmchipN/pwmX
>     - Reverted patch causes new entry to be also created directly in
>       /sys/class/pwm/pwmX
>     - 1st time, exporting pwmX will create an entry in /sys/class/pwm/pwmX
>     - class attributes are added under pwmX folder, such as export, unexport
>       npwm, symlinks. This is wrong as it belongs to pwmchipN. It may cause
>       bad behavior and report wrong values.
>     - when another export happens on another pwmchip, it can't be created
>       (e.g. -EEXIST). This is causing the issue with multiple pwmchip.
> 


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