On 1/15/24 10:37, Jonathan Cameron wrote: > On Sun, 14 Jan 2024 21:04:12 +0100 > Denis Benato <benato.denis96@xxxxxxxxx> wrote: > >> On 1/13/24 18:46, Jonathan Cameron wrote: >>> On Wed, 10 Jan 2024 23:35:01 +0100 >>> Denis Benato <benato.denis96@xxxxxxxxx> wrote: >>> >>>> Hello, >>>> >>>> With this mail I am submitting bug report that is probably related to >>>> iio-trig-hrtimer but there is also the possibility for it to be >>>> specific to bmi160 and bmi323. >>>> >>>> The described problem have been reproduced on my handheld PC (Asus >>>> RC71L) and in another handheld PC with two different gyroscope >>>> drivers: bmi323 (backported by me on v6.7, on RC71L) and bmi160. >>>> >>>> My target hardware (RC71L that yeld to this discovery) has a bmi323 >>>> chip that does not have any interrupt pins reaching the CPU, yet I >>>> need to fetch periodically data from said device, therefore I used >>>> iio-trig-hrtimer: created a trigger, set the device and trigger >>>> sampling frequencies, bound the trigger to the device and enabled >>>> buffer: data is being read and available over /dev/iio:device0. >>>> >>>> While in this state if I suspend my handheld I receive (from dmesg) >>>> the warning reported below and at resume data is not coming out of >>>> the iio device and the hrtimer appears to not be working. If I create >>>> a new trigger and bind the new trigger to said iio device and >>>> re-enable buffer data does come out of /dev/iio:device0 once more, >>>> until the next sleep. >>>> >>>> Since this is important to me I have taken the time to look at both >>>> drivers and iio-trig-hrtimer and I have identified three possible >>>> reasons: >>>> >>>> 1) iio-trig-hrtimer won't work after suspend regardless of how it is >>>> used (this is what I believe is the cause) >>> me too. >> who and how should investigate this issue? Would putting a kprintf in the hrtimer callback be enough to check? > The warning you have pretty much points at this being the problem, but sure > you could add a print there to be absolutely sure. > >> >> >> Just to make sure I understood correctly: is this a separate issue from the warning I receive or are those linked? > > I think it's all one issue. Hello, Sorry for the delay, I was able to find some time just recently. Sadly I don't think anymore this is just one issue: I have setup a proof of concept that at suspend sets a boolean to true and at resume sets the same boolean to false, and on trigger_handler returns IRQ_NONE if the device is sleeping (everything guarded by an additional mutex) and it solved the warning: no more regmap access are being performed after the device is put to sleep, but unfortunately the acquisition does not automatically resume after waking up the device. How shall we proceed? > >>> >>>> 2) iio-trig-hrtimer is stopped by the -ESHTDOWN returned by the >>>> function printing "Transfer while suspended", however that stack >>>> trace does not include function calls related to iio-trig-hrtimer and >>>> this seems less plausible 3) bmi160 and bmi323 appears to be similar >>>> and maybe are sharing a common bug with suspend (this is also why I >>>> have maintainers of those drivers in the recipient list) >>>> >>>> Thanks for your time, patience and understanding, >>> >>> Hi Denis, >>> >>> I suspect this is the legacy of the platform I used to test the hrtimer >>> and similar triggers on never had working suspend and resume (we ripped >>> support for that board out of the kernel a while back now...) >>> Hence those paths were never tested by me and others may not have cared >>> about this particular case. >>> >>> Anyhow, so I think what is going on is fairly simple. >>> >>> There is no way for a driver to indicate to a trigger provided by a separate >>> module / hardware device that it should stop triggering data capture. >>> The driver in question doesn't block data capture when suspended, which >>> would be easy enough to add but doesn't feel like the right solution. >>> >>> So my initial thought is that we should add suspend and resume callbacks to >>> iio_trigger_ops and call them manually from iio device drivers in their >>> suspend and resume callbacks. These would simply pause whatever the >>> trigger source was so that no attempts are made to trigger the use of >>> the device when it is suspended. >>> >>> It gets a little messy though as triggers can be shared between >>> multiple devices so we'd need to reference count suspend and resume >>> for the trigger to make sure we only resume once all consumers of >>> the trigger have said they are ready to cope with triggers again. >>> >>> As mentioned, the alternative would be to block the triggers at ingress >>> to the bmi323 and bmi160 drivers. There may be a helpful pm flag that could >>> be used but if not, then setting an is_suspended flag under the data->mutex >>> to avoid races. and reading it in the trigger_handler to decide whether >>> to talk to the device should work. >> I was thinking of doing this too, but I don't know if adding a mutex to frequently invoked functions is going to introduce some timing problems and so I was waiting for some comments on that matter. If nothing bad is expected I can surely try it. >>> >>> I'd kind of like the generic solution of actually letting the trigger >>> know, but not sure how much work it would turn out to be. Either way there >>> are a lot of drivers to fix this problem in as in theory most triggers can >>> be used with most drivers that support buffered data capture. >>> There may also be fun corners where a hardware trigger from one IIO >>> device A is being used by another B and the suspend timing is such that B >>> finishing with the trigger results in A taking an action (in the try_reenable >>> callback) that could result in bus traffic. >>> That one is going to be much more fiddly to handle than the simpler case >>> you have run into. >> Since more and more handheld PCs are coming and provided many vendors such as >> asus tends to improve what they did built on previous generations I think a >> general solution would be desirable. >> >> Plus there are handheld PCs that does not yet have a driver (bmi270) or are >> using an existing one and it would be very difficult to fix it in every of >> them as of now, in the future I fear it will become almost impossible or >> extremely time consuming as market expands. > > Both solutions require specific calls to be added to every driver that might > encounter this - so most drivers that support triggers other than the ones > they supply. > >>> >>> Thanks for the detailed bug report btw. To get it fixed a few >>> questions: >>> 1) Are you happy to test proposed fixes? >>> 2) Do you want to have a go at fixing it yourself? (I'd suggest trying >>> the fix in the bmi323 driver first rather than looking at the other >>> solution) >>> If we eventually implement the more general version, then a bmi323 >>> additional protection against this problem would not be a problem. >>> >>> Clearly I'd like the answers to be yes to both questions, but up to you! >>> >>> Jonathan >>> >>> >> Hello Jonathan and thank you kindly for you answer, >> >> I am very interested in the iio ecosystem as in those aforementioned >> handheld PCs the gyroscope plays the role as a mouse so it's a pretty >> important input device. >> >> I am writing to lkml not just as a single developer, but as part of a >> larger community in this matter: this means we will be able to test >> any solution and in more than just one hardware. >> >> To answers your questions: >> 1) yes, we all will be very happy to >> 2) as I am very busy right now I might be unable to do that immediately, >> but I will surely do it if one general solution cannot be found or is impractical. >> >> As of my limited knowledge the number of drivers now existing that are affected >> are 2, and the number of drivers that will be affected, once the driver is >> written, will be at least 3. > > The problem appears to be general unfortunately. > > I'll have to see if I can fire up something where I can actually test solutions > and I'm afraid I also don't have a lot of time at the moment. > Perhaps I can find time in the next few weeks to hack together a prototype > for one of the drivers you can test. > > Jonathan > >> >> Thank you very much for your answer, >> Denis >> > Thank you for you time and patience, Denis
