Re: iio: iio-trig-hrtimer bug on suspend/resume when used with bmi160 and bmi323

[Denis Benato]

On 6/2/24 18:08, Jonathan Cameron wrote:
> On Thu, 30 May 2024 16:07:22 +0200
> Denis Benato <benato.denis96@xxxxxxxxx> wrote:
> 
>> 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?
> 
> It's been a while (and a busy day of reviewing) so I'm struggling
> a bit with the best away forwardHello,

Don't worry about it, I don't have much time available either. That stuff is as precious as gold! Thank you kindly for your time!
> 
> A hackyish approach might be to mask the interrupt at device side
> (fake interrupt used as part of the tree from a trigger to a pollfunc).
> A tidy wrapped up version of this might be the best route forwards
> though it won't currently stop the hrtimer merrily poking interrupts
> at no oneI am sorry but I am not sure I understood this correctly: do you mean having something "in-between" iio-trig-hrtimer and the target iio device and use that to selectively poll the device? 
> 
> As a hack, could you try having your suspend call disable_irq() on
> the irq found in iio_dev->poll_func->irq and reenable it in resume?
> That might be sufficient.
I used disable_irq and enable_irq as suggested and it works perfectly: I tested it four times and all four times (in a row) data flow resumed after s2idle-suspending the device.

I can do more testing, but this is already looking very good and I'm happy (I don't have knowledge about iio internals so I am unable to tell if what I did will introduce some race conditions).

As a reference I leave here the github link to the branch I have been experimenting with: https://github.com/NeroReflex/linux/commits/bmi323-pollfunc/ (Please don't mind that proof-of-concept code being copied and partially commented from bmc150-accel).

No errors are printed out and combining that info with the fact it's now working it can only means pollfunc and irq are both non-NULL and non-zero at both suspend and resume.
> 
> Check poll_func goes somewhere first though and that irq is > 0
> I think that will call iio_trig_subirq_mask() which should block
> any further interrupts until it's unmasked again.
> 
> We'll need to ensure this doesn't race with pollfunc going away though
> which will make it more complex, but the above test should tell us
> if there is a fairly smooth path to making this work.
> 
> I'll try and find time to do some testing myself, but it won't be
> for a few weeks :(
> 
> Thanks,
> 
> Jonathan
Thank you again for your guidance,
Denis Benato
> 
> 
>>>   
>>>>>     
>>>>>> 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
>