linux-kernel - Re: [PATCH v13 13/35] drm/tegra: gr2d: Support generic power domain and runtime PM

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Date:   Tue, 5 Oct 2021 20:16:11 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Nishanth Menon <nm@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Michael Turquette <mturquette@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-staging@...ts.linux.dev, linux-pwm@...r.kernel.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        David Heidelberg <david@...t.cz>
Subject: Re: [PATCH v13 13/35] drm/tegra: gr2d: Support generic power domain
 and runtime PM

...
>> It's not a problem to change this patchset. The problem is that if
>> you'll grep mainline for 'pm_runtime_disable', you will find that there
>> are a lot of drivers in a potential trouble.
> 
> Let's start by fixing this patchset, please - then we can consider
> what to do with the other cases separately.

Yeah, should be better to discuss it separately.

...
>>  void __pm_runtime_disable(struct device *dev, bool check_resume)
>>  {
>> +       flush_work(&dev->power.work);
>> +
> 
> What about the latency this may introduce? I am not sure that is
> acceptable here!?

I'm not aware about any code which relies on the original 'cancelling'
behaviour, perhaps Rafael should have more insight.

...
>> The sysfs rpm-forbid is a separate problem and it's less troublesome
>> since it requires root privileges. It's also not something that
>> userspace touches casually. For now I don't know what could be done
>> about it.
> 
> As I said, the common method to address this problem is to run the
> following sequence:
> 
> pm_runtime_get_sync()
> "power off the device"
> pm_runtime_disable()
> pm_runtime_put_noidle()
> 
> This works even if user space, via sysfs, has triggered a call to
> pm_runtime_forbid(). Or doesn't it?
> 
> If you don't like it, pm_runtime_force_suspend() should work too, at
> least for your cases, I believe.

I'll update the patches, thank you.