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[34.143.156.49]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-73242546301sm9261922b3a.33.2025.02.17.21.45.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Feb 2025 21:45:49 -0800 (PST) Date: Tue, 18 Feb 2025 11:15:40 +0530 From: Ajay Agarwal To: "Rafael J. Wysocki" Cc: Brian Norris , Oliver Neukum , "Rafael J. Wysocki" , Vincent Whitchurch , "jic23@kernel.org" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-iio@vger.kernel.org" , Brian Norris , Joy Chakraborty , Vamshi Gajjela , Manu Gautam Subject: Re: PM runtime_error handling missing in many drivers? Message-ID: References: <1937b65c-36c0-5475-c745-d7285d1a6e25@suse.com> <5c37ee19-fe2c-fb22-63a2-638e3dab8f7a@suse.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Feb 18, 2025 at 11:07:19AM +0530, Ajay Agarwal wrote: > On Mon, Feb 17, 2025 at 09:23:18PM +0100, Rafael J. Wysocki wrote: > > On Mon, Feb 17, 2025 at 4:49 AM Ajay Agarwal wrote: > > > > > > On Wed, Feb 12, 2025 at 08:29:34PM +0100, Rafael J. Wysocki wrote: > > > > On Tue, Feb 11, 2025 at 11:21 PM Brian Norris wrote: > > > > > > > > > > Hi Ajay, > > > > > > > > > > On Mon, Feb 10, 2025 at 09:02:41AM +0530, Ajay Agarwal wrote: > > > > > > On Wed, Jul 27, 2022 at 06:31:48PM +0200, Rafael J. Wysocki wrote: > > > > > > > On Wed, Jul 27, 2022 at 10:08 AM Oliver Neukum wrote: > > > > > > > > On 26.07.22 17:41, Rafael J. Wysocki wrote: > > > > > > > > > Well, in general suspending or resuming a device is a collaborative > > > > > > > > > effort and if one of the pieces falls over, making it work again > > > > > > > > > involves fixing up the failing piece and notifying the others that it > > > > > > > > > is ready again. However, that part isn't covered and I'm not sure if > > > > > > > > > it can be covered in a sufficiently generic way. > > > > > > > > > > > > > > > > True. But that still cannot solve the question what is to be done > > > > > > > > if error handling fails. Hence my proposal: > > > > > > > > - record all failures > > > > > > > > - heed the record only when suspending > > > > > > > > > > > > > > I guess that would boil down to moving the power.runtime_error update > > > > > > > from rpm_callback() to rpm_suspend()? > > > > > > Resuming this discussion. One of the ways the device drivers are > > > > > > clearing the runtime_error flag is by calling pm_runtime_set_suspended > > > > > > [1]. > > > > > > > > I personally think that jumping on a 2.5 years old thread is not a > > > > good idea. It would be better to restate the problem statement and > > > > provide the link to the previous discussion. > > > > > > > > > > To me, it feels weird that a device driver calls pm_runtime_set_suspended > > > > > > if the runtime_resume() has failed. It should be implied that the device > > > > > > is in suspended state if the resume failed. > > > > > > > > > > > > So how really should the runtime_error flag be cleared? Should there be > > > > > > a new API exposed to device drivers for this? Or should we plan for it > > > > > > in the framework itself? > > > > > > > > > > While the API naming is unclear, that's exactly what > > > > > pm_runtime_set_suspended() is about. Personally, I find it nice when a > > > > > driver adds the comment "clear runtime_error flag", because otherwise > > > > > it's not really obvious why a driver has to take care of "suspending" > > > > > after a failed resume. But that's not the biggest question here, IMO. > > > > > > > > > > The real reson I pointed you at this thread was because I think it's > > > > > useful to pursue the proposal above: to avoid setting a persistent > > > > > "runtime_error" for resume failures. This seems to just create a pitfall > > > > > for clients, as asked by Vincent and Oliver upthread. > > > > > > > > > > And along this line, there are relatively few drivers that actually > > > > > bother to reset this error flag ever (e.g., commit f2bc2afe34c1 > > > > > ("accel/ivpu: Clear runtime_error after pm_runtime_resume_and_get() > > > > > fails")). > > > > > > > > > > So to me, we should simply answer Rafael's question: > > > > > > > > > > (repeated:) > > > > > > > I guess that would boil down to moving the power.runtime_error update > > > > > > > from rpm_callback() to rpm_suspend()? > > > > > > > > > > Yes, I think so. (Although I'm not sure if this leaves undesirable spam > > > > > where persistent .runtime_resume() failures occur.) > > > > > > > > > > ...and then write/test/submit such a patch, provided it achieves the > > > > > desired results. > > > > > > > > > > Unless of course one of the thread participants here has some other > > > > > update in the intervening 2.5 years, or if Rafael was simply asking the > > > > > above rhetorically, and wasn't actually interested in fielding such a > > > > > change. > > > > > > > > The reason why runtime_error is there is to prevent runtime PM > > > > callbacks from being run until something is done about the error, > > > > under the assumption that running them in that case may make the > > > > problem worse. > > > > > > > > I'm not sure if I see a substantial difference between suspend and > > > > resume in that respect: If any of them fails, the state of the device > > > > is kind of unstable. In particular, if resume fails and the device > > > > doesn't actually resume, something needs to be done about it or it > > > > just becomes unusable. > > > > > > > > Now, the way of clearing the error may not be super-convenient, which > > > > was a bit hard to figure out upfront, so I'm not against making any > > > > changes as long as there are sufficient reasons for making them. > > > > > > I am thinking if we can start with a change to not check runtime_error > > > in rpm_resume, and let it go through even if the previous rpm_resume > > > attempt failed. Something like this: > > > > > > ``` > > > static int rpm_resume(struct device *dev, int rpmflags) > > > trace_rpm_resume(dev, rpmflags); > > > > > > repeat: > > > - if (dev->power.runtime_error) { > > > - retval = -EINVAL; > > > - } else if (dev->power.disable_depth > 0) { > > > + if (dev->power.disable_depth > 0) { > > > if (dev->power.runtime_status == RPM_ACTIVE && > > > dev->power.last_status == RPM_ACTIVE) > > > retval = 1; > > > ``` > > > > > > I think setting the runtime_error in rpm_callback, i.e. for both resume > > > and suspend is still a good idea for book-keeping purposes, e.g. the > > > user reading the runtime_status of the device from sysfs. > > > > What would be the benefit of this change? > The benefit would be that the runtime_resume would be re-attempted even if > the previous attempt failed. Actually, I wanted to propose the removal of `runtime_error` flag completely from the code. But it sounded too disruptive to me. Hence, I proposed the milder patch of removal of `runtime_error` check from rpm_resume so that the drivers do not have to call `pm_runtime_set_suspended` explicitly. Basically, we still do not have a good solution for the situation where one of the ancestors fails to resume. We do not know how to make the ancestor working again. But I guess a re-attempt is better than not doing anything about it?