linux-kernel - Re: [PATCH v2] thermal: imx: implement runtime PM support

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Date:   Thu, 21 Oct 2021 09:44:56 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Petr Benes <petrben@...il.com>,
        Michal Vokáč <michal.vokac@...ft.com>,
        linux-pm@...r.kernel.org, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Amit Kucheria <amitk@...nel.org>, linux-kernel@...r.kernel.org,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        David Jander <david@...tonic.nl>,
        Zhang Rui <rui.zhang@...el.com>,
        Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] thermal: imx: implement runtime PM support

On Thu, Oct 21, 2021 at 09:41:35AM +0200, Daniel Lezcano wrote:
> On 21/10/2021 09:20, Oleksij Rempel wrote:
> > Hi Petr,
> > 
> > On Wed, Oct 20, 2021 at 05:53:03PM +0200, Petr Benes wrote:
> >> On Wed, 20 Oct 2021 at 07:05, Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> >>>
> >>> Hi Petr and Michal,
> >>>
> >>> I forgot to add you for v2 in CC. Please test/review this version.
> >>
> >> Hi Oleksij,
> >>
> >> It works good. with PM as well as without PM. The only minor issue I found is,
> >> that the first temperature reading (when the driver probes) fails. That is
> >> (val & soc_data->temp_valid_mask) == 0) holds true. How does
> >> pm_runtime_resume_and_get() behave in imx_thermal_probe()?
> >> Does it go through imx_thermal_runtime_resume() with usleep_range()?
> > 
> > On the first temperature reading, the PM and part of HW is not
> > initialized. Current probe sequence is racy and has at least following
> > issues:
> > - thermal_zone_device_register is executed before HW init was completed.
> >   It kind of worked before my patch, becaus part of reinit was done by
> >   temperature init. It  worked, since the irq_enabled flag was not set,
> >   but potentially would run enable_irq() two times if device is
> >   overheated on probe.
> > - the imx_thermal core is potentially disable after first race
> >   condition:
> >   CPU0					CPU1
> >   thermal_zone_device_register()
> > 					imx_get_temp()
> >   					irq_enabled == false
> > 						power_up
> > 						read_temp
> >   power_up
> >   						power_down
> >   irq_enabled = true;
> > 
> >   ... at this point imx_thermal is powered down for some amount of time,
> >   over temperature IRQ will not be triggered for some amount of time.
> > 
> > - if some part after thermal_zone_device_register() would fail or
> >   deferred, the worker polling temperature will run in to NULL pointer.
> >   This issue already happened...
> > 
> > After migrating to runtime PM, one of issues started to be visible even
> > on normal conditions.
> > I'll send one more patch with reworking probe sequence.
> 
> Are you planning to send a v3 with this patch? Or a separate patch?

I'm OK with both variants. What do you prefer?

I'll do i on top of PM patch to reduce refactoring overhead, if you OK
about it.

Regards,
Oleksij
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