Re: [PATCH v3 100/108] gpio: mvebu: Make use of devm_pwmchip_alloc() function

[Bartosz Golaszewski <brgl@bgdev.pl>]

On Fri, Nov 24, 2023 at 1:14 PM Thierry Reding <thierry.reding@gmail.com> wrote:
>
> On Wed, Nov 22, 2023 at 11:36:19AM +0100, Bartosz Golaszewski wrote:
> > On Wed, Nov 22, 2023 at 10:05 AM Uwe Kleine-König
> > <u.kleine-koenig@pengutronix.de> wrote:
> > >
> > > Hello Bart,
> > >
> > > On Tue, Nov 21, 2023 at 05:11:11PM +0100, Uwe Kleine-König wrote:
> > > > On Tue, Nov 21, 2023 at 03:02:39PM +0100, Bartosz Golaszewski wrote:
> > > > > Eh... I had a talk at LPC where I explained why I really dislike this
> > > > > approach but I guess this ship has sailed now and it's not a subsystem
> > > > > where I have any say anyway.
> > > >
> > > > Is there a record of your talk? I'm open to hear your arguments.
> > >
> > > I found your slides at
> > > https://lpc.events/event/17/contributions/1627/attachments/1258/2725/Linux%20Plumbers%20Conference%202023.pdf
> > >
> >
> > My talk is here: https://www.youtube.com/watch?v=VxaAorwL89c&t=29310s
>
> I've been watching this along with Laurent's talk from last year (and I
> guess I should probably also go through Wolfram's patch from earlier
> this year) and I really like what you presented. It also sounds like
> there was a lot of support across various audience members, so I think
> it'd be good to rally around such a common pattern so we can start to
> improve things on a more wide basis.
>
> Given that this wasn't very long ago, I wouldn't expect that much work
> has happened yet on the resmgr library. However, I think it would fit
> very well both with how PWM works today and with what Uwe has in mind
> for the character device support.
>
> Thierry

Hi Thierry,

Thanks for the kind words. No work has been done so far other than
thinking about the possible API. I'm currently in the process of
trying to fix the object life-time and concurrent access in GPIO -
mostly improving the dire locking situation. My goal is to implement
all I spoke about in GPIO first and then try to generalize it to some
other subsystem like what Greg KH suggested.

I've already got support from Wolfram on that and we of course could
use any help we can get.

I admit I've been quite busy but I do plan on going through Uwe's
series next week and maybe running tests similar to what I have for
GPIO on it. I'm quite certain (correct me if I'm wrong) that this
series doesn't improve the locking (specifically hot-unplug events
during API calls). I think that my proposal has the advantage of
having the pointer to the implementation in the "wrapper" which can be
easily protected with RCU.

Uwe: do you have a solution for device removal concurrent with API
calls when using your approach?

Bart