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[79.139.163.57]) by smtp.googlemail.com with ESMTPSA id l9sm886038lje.32.2021.10.04.08.57.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Oct 2021 08:57:12 -0700 (PDT) Subject: Re: [PATCH v13 13/35] drm/tegra: gr2d: Support generic power domain and runtime PM To: Ulf Hansson , "Rafael J. Wysocki" Cc: Thierry Reding , Jonathan Hunter , Viresh Kumar , Stephen Boyd , Peter De Schrijver , Mikko Perttunen , Peter Chen , Lee Jones , =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= , Nishanth Menon , Adrian Hunter , Michael Turquette , Linux Kernel Mailing List , linux-tegra , Linux PM , Linux USB List , linux-staging@lists.linux.dev, linux-pwm@vger.kernel.org, linux-mmc , dri-devel , DTML , linux-clk , Mark Brown , Vignesh Raghavendra , Richard Weinberger , Miquel Raynal , Lucas Stach , Stefan Agner , Mauro Carvalho Chehab , David Heidelberg References: <20210926224058.1252-1-digetx@gmail.com> <20210926224058.1252-14-digetx@gmail.com> <8d75436d-864a-7ce0-ba53-daa8b663035a@gmail.com> From: Dmitry Osipenko Message-ID: Date: Mon, 4 Oct 2021 18:57:11 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 04.10.2021 14:01, Ulf Hansson пишет: > On Fri, 1 Oct 2021 at 21:00, Dmitry Osipenko wrote: >> >> 01.10.2021 17:55, Ulf Hansson пишет: >>> On Fri, 1 Oct 2021 at 16:29, Dmitry Osipenko wrote: >>>> >>>> 01.10.2021 16:39, Ulf Hansson пишет: >>>>> On Mon, 27 Sept 2021 at 00:42, Dmitry Osipenko wrote: >>>>>> >>>>>> Add runtime power management and support generic power domains. >>>>>> >>>>>> Tested-by: Peter Geis # Ouya T30 >>>>>> Tested-by: Paul Fertser # PAZ00 T20 >>>>>> Tested-by: Nicolas Chauvet # PAZ00 T20 and TK1 T124 >>>>>> Tested-by: Matt Merhar # Ouya T30 >>>>>> Signed-off-by: Dmitry Osipenko >>>>>> --- >>>>>> drivers/gpu/drm/tegra/gr2d.c | 155 +++++++++++++++++++++++++++++++++-- >>>>> >>>>> [...] >>>>> >>>>>> static int gr2d_remove(struct platform_device *pdev) >>>>>> @@ -259,15 +312,101 @@ static int gr2d_remove(struct platform_device *pdev) >>>>>> return err; >>>>>> } >>>>>> >>>>>> + pm_runtime_dont_use_autosuspend(&pdev->dev); >>>>>> + pm_runtime_disable(&pdev->dev); >>>>> >>>>> There is no guarantee that the ->runtime_suspend() has been invoked >>>>> here, which means that clock may be left prepared/enabled beyond this >>>>> point. >>>>> >>>>> I suggest you call pm_runtime_force_suspend(), instead of >>>>> pm_runtime_disable(), to make sure that gets done. >>>> >>>> The pm_runtime_disable() performs the final synchronization, please see [1]. >>>> >>>> [1] >>>> https://elixir.bootlin.com/linux/v5.15-rc3/source/drivers/base/power/runtime.c#L1412 >>> >>> pm_runtime_disable() end up calling _pm_runtime_barrier(), which calls >>> cancel_work_sync() if dev->power.request_pending has been set. >>> >>> If the work that was punted to the pm_wq in rpm_idle() has not been >>> started yet, we end up just canceling it. In other words, there are no >>> guarantees it runs to completion. >> >> You're right. Although, in a case of this particular patch, the syncing >> is actually implicitly done by pm_runtime_dont_use_autosuspend(). >> >> But for drivers which don't use auto-suspend, there is no sync. This >> looks like a disaster, it's a very common pattern for drivers to >> 'put+disable'. >> >>> Moreover, use space may have bumped the usage count via sysfs for the >>> device (pm_runtime_forbid()) to keep the device runtime resumed. >> >> Right, this is also a disaster in a case of driver removal. >> >>>> Calling pm_runtime_force_suspend() isn't correct because each 'enable' >>>> must have the corresponding 'disable'. Hence there is no problem here. >>> >>> pm_runtime_force_suspend() calls pm_runtime_disable(), so I think that >>> should be fine. No? >> >> [adding Rafael] >> >> Rafael, could you please explain how drivers are supposed to properly >> suspend and disable RPM to cut off power and reset state that was >> altered by the driver's resume callback? What we're missing? Is Ulf's >> suggestion acceptable? >> >> The RPM state of a device is getting reset on driver's removal, hence >> all refcounts that were bumped by the rpm-resume callback of the device >> driver will be screwed up if device is kept resumed after removal. I >> just verified that it's true in practice. > > Note that, what makes the Tegra drivers a bit special is that they are > always built with CONFIG_PM being set (selected from the "SoC" > Kconfig). > > Therefore, pm_runtime_force_suspend() can work for some of these > cases. Using this, would potentially avoid the driver from having to > runtime resume the device in ->remove(), according to the below > generic sequence, which is used in many drivers. > > pm_runtime_get_sync() > clk_disable_unprepare() (+ additional things to turn off the device) > pm_runtime_disable() > pm_runtime_put_noidle() 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. I'm proposing that we should change pm_runtime_disable() to perform the syncing with this oneliner: diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c index ec94049442b9..5c9f28165824 100644 --- a/drivers/base/power/runtime.c +++ b/drivers/base/power/runtime.c @@ -1380,6 +1380,8 @@ EXPORT_SYMBOL_GPL(pm_runtime_barrier); */ void __pm_runtime_disable(struct device *dev, bool check_resume) { + flush_work(&dev->power.work); + spin_lock_irq(&dev->power.lock); if (dev->power.disable_depth > 0) { Objections? 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.