Re: [PATCH] pwm: Create device class for pwm channels

[David Hsu]

On Wed, Jun 15, 2016 at 7:37 AM, Thierry Reding
<thierry.reding@xxxxxxxxx> wrote:
> On Tue, Jun 14, 2016 at 07:12:04PM -0700, Greg KH wrote:
>> From: David Hsu <davidhsu@xxxxxxxxxx>
>>
>> Pwm channels don't send uevents when exported, this change adds the
>> channels to a pwm class and set their device type to pwm_channel so
>> uevents are sent.
>>
>> To do this properly, the device names need to change to uniquely
>> identify a channel.  This change is from pwmN to pwm-(chip->base):N
>>
>> Signed-off-by: David Hsu <davidhsu@xxxxxxxxxx>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> ---
>>  Documentation/pwm.txt |    6 ++++--
>>  drivers/pwm/sysfs.c   |   15 ++++++++++++---
>>  2 files changed, 16 insertions(+), 5 deletions(-)
>>
>> Note, this patch came from David with his work on a system that has
>> dynamic PWM devices and channels, and we needed some way to tell
>> userspace what is going on when they are added or removed.  If anyone
>> knows any other way of doing this that does not involve changing the pwm
>> names, please let us know.
>
> Is it truly PWM channels that dynamically appear and disappear? I'd be
> interested in how that's achieved, because there are probably other
> issues that will manifest if you do that. Do you have a pointer to the
> work that David's been undertaking? Generally some more context on the
> use-case would be helpful here.

Only PWM devices are dynamic, the number of channels exposed by
devices do not change after they've been added to the system.

>
> Also I'd prefer if this avoided using chip->base here, because it exists
> purely for legacy purposes and is supposed to go away eventually.
>
> Thierry

Would using dev_name(parent) be an acceptable alternative?

Thanks,
David