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. > > > >> 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 >
