Re: [PATCH v1 000/101] pwm: Fix lifetime issues for pwm_chips

[Thierry Reding <thierry.reding@gmail.com>]

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On Tue, Aug 08, 2023 at 07:17:50PM +0200, Uwe Kleine-König wrote:
> Hello,
> 
> this series addresses the issues I reported already earlier to this
> list[1]. It is based on pwm/for-next and several patches I already sent
> out, too. Maybe some of these have to be reworked (e.g. Thierry already
> signalled not to like the patches dropping runtime error messages) but
> in the expectation that I will have to create a v2 for this series, too
> and it actually fixes a race condition, I sent the patches out for
> review anyhow. For the same reason I didn't Cc: all the individual
> maintainers.
> 
> If you want to actually test I suggest you fetch my complete history
> from
> 
> 	https://git.pengutronix.de/git/ukl/linux pwm-lifetime-tracking
> 
> . 
> 
> In the end drivers have to allocate their pwm_chip using
> pwmchip_alloc(). This is important for the memory backing the pwm_chip
> being able to have a longer life than the driver.

Couldn't we achieve the same thing by just making sure that drivers
don't use any of the device-managed APIs to do this? That seems like a
slightly less intrusive way of doing things.

> The motivation for this series is to prepare the pwm framework to add a
> character device for each pwm_chip for easier and faster access to PWMs
> from userspace compared to the sysfs API. For such an extension proper
> lifetime tracking is important, too, as such a device can still be open
> if a PWM disappears.

As I mentioned before, I'd like to see at least a prototype of the
character device patches before I merge this series. There's a whole lot
of churn here and without the character device support it's hard to
justify.

I have a couple more detailed comments, but I'll leave those in response
to some of the other patches for better context.

Thierry

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