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

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Message-ID: <CAPwXO5anM809k+wuSYU9LR9vLAyutaMNo6kceCHOZHPmZUbnUw@mail.gmail.com>
Date:   Mon, 15 Nov 2021 16:02:07 +0100
From:   Petr Benes <petrben@...il.com>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Michal Vokáč <michal.vokac@...ft.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-pm@...r.kernel.org, Fabio Estevam <festevam@...il.com>,
        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>,
        Shawn Guo <shawnguo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] thermal: imx: implement runtime PM support

Hi Oleksij,

On Thu, 11 Nov 2021 at 10:16, Oleksij Rempel <o.rempel@...gutronix.de> wrote:
>
> On Wed, Nov 10, 2021 at 11:07:31AM +0100, Michal Vokáč wrote:
> > On 25. 10. 21 13:06, Petr Benes wrote:
> > > Hi Oleksij,
> > >
> > > On Thu, 21 Oct 2021 at 19:21, Oleksij Rempel <o.rempel@...gutronix.de> 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()?
> > > >
> > > > How exactly did you reproduce it? Even more or less understanding how
> > >
> > > I just placed my debug print into get_temp()
> > >
> > >      if ((val & soc_data->temp_valid_mask) == 0) {
> > >          dev_dbg(&tz->device, "temp measurement never finished\n");
> > >          printk("Wrong temperature reading!!!!!!\n");
> > >          return -EAGAIN;
> > >      }
> > >
> > > > this can potentially happen, i never had this issue on my HW. Is it something
> > > > HW specific?
> > >
> > > IMHO it is just product of the following sequence:
> > >
> > > pm_runtime_set_active(&pdev->dev);
> > > pm_runtime_enable(data->dev);
> > > pm_runtime_resume_and_get(data->dev);
> > > thermal_zone_device_enable(data->tz);
> > >
> > > With assumption imx_thermal_runtime_resume() didn't run,
> > > hence the sensor didn't get enough time to come up.
> > >
> > > I didn't have time to spend it on and you have better knowledge of the
> > > area. If it is not that straightforward I can try to diagnose it better.
> > >
> > Hi Oleksij,
> > Did you manage to further debug and reproduce this problem?
> > Do you plan to send the v3?
> >
> > Regarding your question about the HW - this problem occured once we
> > upgraded the SoC on our SBC from i.MX6DL to i.MX6Q/QP. With the DualLite
> > we never had this problem but the Quad is getting hot quite fast.
> > We have pretty limited cooling options so the core is operated at its
> > upper temperature limits when fully loaded.
>
> Hi Michal,
>
> Sorry, I was busy and lost this topic from my radar. I was not able to
> reproduce it on my i.MX6Q and i.MX6QP died after other thermal voltage
> experiments. Please, if you able to reproduce it, try to investigate
> what is wrong, for example increasing wakeup time and/or and tracing
> sleap/wake/get sequences.

Seems it is just as easy as calling usleep_range(20, 50) when you switch on
the sensor and enable temperature measurement in imx_thermal_probe().
So, we are sure the sensor is configured and _ready_.

You call pm_runtime_set_active(), pm_runtime_enable(), and
pm_runtime_resume_and_get(). The last one doesn't call the resume
callback (which correctly handles waiting for the sensor) as the device
is already active.

On some SoCs the timing leads to a failure of the temperature readout
in thermal_zone_device_enable() which follows. I've seen it on i.MX6DL,
but cannot reproduce it on i.MX6QP for example.

Regards,
Petr

>
> Regards,
> Oleksij
> --
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