On Tue, 26 Nov 2024 at 18:18, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > On Tue, Nov 26, 2024 at 05:22:20PM +0100, Ricardo Ribalda wrote: > > On Mon, 25 Nov 2024 at 15:02, Hans de Goede wrote: > > > On 25-Nov-24 2:39 PM, Ricardo Ribalda wrote: > > > > On Mon, 25 Nov 2024 at 13:25, Hans de Goede wrote: > > > >> On 9-Nov-24 5:29 PM, Ricardo Ribalda wrote: > > > >> > > > >> <snip> > > > >> > > > >>>> I have been discussing UVC power-management with Laurent, also > > > >>>> related to power-consumption issues caused by libcamera's pipeline > > > >>>> handler holding open the /dev/video# node as long as the camera > > > >>>> manager object exists. > > > >> > > > >> <snip> > > > >> > > > >>>> Here is what I have in mind for this: > > > >>>> > > > >>>> 1. Assume that the results of trying a specific fmt do not change over time. > > > >>>> > > > >>>> 2. Only allow userspace to request fmts which match one of the enum-fmts -> > > > >>>> enum-frame-sizes -> enum-frame-rates tripplet results > > > >>>> (constrain what userspace requests to these) > > > >>>> > > > >>>> 3. Run the equivalent of tryfmt on all possible combinations (so the usaul > > > >>>> 3 levels nested loop for this) on probe() and cache the results > > > >>>> > > > >>>> 4. Make try_fmt / set_fmt not poweron the device but instead constrain > > > >>>> the requested fmt to one from our cached fmts > > > >>>> > > > >>>> 5. On stream-on do the actual power-on + set-fmt + verify that we get > > > >>>> what we expect based on the cache, and otherwise return -EIO. > > > >>> > > > >>> Can we start powering up the device during try/set fmt and then > > > >>> implement the format caching as an improvement? > > > >> > > > >> Yes, actually looking at how complex this is when e.g. also taking > > > >> controls into account I think that taking small steps is a good idea. > > > >> > > > >> I have lately mostly been working on sensor drivers where delaying > > > >> applying format settings + all controls to stream-on is normal. > > > >> > > > >> So that is the mental model I'm applying to uvc here, but that might > > > >> not be entirely applicable. > > > >> > > > >>> Laurent mentioned that some cameras missbehave if a lot of controls > > > >>> are set during probing. I hope that this approach does not trigger > > > >>> those, and if it does it would be easier to revert if we do the work > > > >>> in two steps. > > > >> > > > >> Ack, taking small steps sounds like a good plan. > > > >> > > > >> <snip> > > > >> > > > >>>> This should also make camera enumeration faster for apps, since > > > >>>> most apps / frameworks do the whole 3 levels nested loop for this > > > >>>> on startup, for which atm we go out to the hw, which now instead > > > >>>> will come from the fmts cache and thus will be much much faster, > > > >>>> so this should lead to a noticeable speedup for apps accessing UVC > > > >>>> cameras which would be another nice win. > > > >>>> > > > >>>> Downside is that the initial probe will take longer see we do > > > >>>> all the tryfmt-s there now. But I think that taking a bit longer > > > >>>> to probe while the machine is booting should not be an issue. > > > >>> > > > >>> How do you pretend to handle the controls? Do you plan to power-up the > > > >>> device during s_ctrl() or set them only during streamon()? > > > >>> If we power-up the device during s_ctrl we need to take care of the > > > >>> asynchronous controls (typically pan/tilt/zoom), The device must be > > > >>> powered until the control finishes, and the device might never reply > > > >>> control_done if the firmware is not properly implemented. > > > >>> If we set the controls only during streamon, we will break some > > > >>> usecases. There are some video conferencing equipment that do homing > > > >>> during streamoff. That will be a serious API breakage. > > > >> > > > >> How to handle controls is a good idea. > > > >> > > > >> Based on my sensor experience my initial idea was to just cache them > > > >> all. Basically make set_ctrl succeed but do not actually do anyhing > > > >> when the camera is not already powered on and then on stream-on call > > > >> __v4l2_ctrl_handler_setup() to get all current values applied. > > > >> > > > >> But as you indicate that will likely not work well with async controls, > > > >> although we already have this issue when using v4l2-ctl from the cmdline > > > >> on such a control and that seems to work fine. > > > > > > > > ----- > > > >> Just because we allow > > > >> the USB connection to sleep, does not mean that the camera cannot finish > > > >> doing applying the async control. > > > >> > > > > Not sure what you mean with this sentence. Could you explain it > > > > differently? Sorry > > > > > > > >> But I can see how some cameras might not like this and having 2 different > > > >> paths for different controls also is undesirable. > > > >> > > > >> Combine that with what Laurent said about devices not liking it when > > > >> you set too much controls in a short time and I do think we need to > > > >> immediately apply ctrls. > > > >> > > > >> I see 2 ways of doing that: > > > >> > > > >> 1. Use pm_runtime_set_autosuspend_delay() with a delay of say 1 second > > > >> and then on set_ctrl do a pm_runtime_get_sync() + > > > >> pm_runtime_put_autosuspend() giving the camera 1 second to finish > > > >> applying the async ctrl (which might not be enough for e.g homing) + > > > >> also avoid doing suspend + resume all the time if multiple ctrls are send > > > > > > > > What about 1.5: > > > > > > > > during s_ctrl(): > > > > usb_autopm_get_interface() > > > > if the control is UVC_CTRL_FLAG_ASYNCHRONOUS. > > > > usb_autopm_get_interface() > > > > set the actual control in the hardware > > > > usb_autopm_put_interface() > > > > > > > > during uvc_ctrl_status_event(): > > > > usb_autopm_put_interface() > > > > > > How do we match this to the usb_autopm_get_interface() > > > call ? At a minimum we would need some counter to > > > track pending (not acked through status interrupt urb) > > > async control requests and only do the put() if that > > > counter >= 1 (and then decrease the counter). > > > > > > We don't want to do unbalanced puts here in case of > > > buggy cameras sending unexpected / too many > > > ctrl status events. > > We would need a counter indeed, which is a big red flag of bad > engineering. It will be fragile at best. > > > > > during close(): > > > > send all the missing usb_autopm_put_interface() > > > > > > Except for my one remark this is an interesting > > > proposal. > > > > I have just upload a patchset implementing this. I tried > > v4l2-compliance and using the camera app. > > > > I think it looks promissing > > > > Shall we move the discussion there? > > > > https://lore.kernel.org/linux-media/20241126-uvc-granpower-ng-v1-0-6312bf26549c@xxxxxxxxxxxx/T/#t > > You're sending too many patch series too quickly, even before we can > come to an agreement on any item being discussed. Experimenting is > helpful, but if we keep moving the discussion from one series to the > next, that won't work. Let's keep it here, and focus on one problem at a > time, or the end result will be slower merging of the patches. I'd argue that it is better to discuss power management in a series called "uvcvideo: Implement Granular Power Saving" than in another called "media: uvcvideo: Implement the Privacy GPIO as a subdevice" Those two problems are orthogonal. I also believe that Hans agreed that that approach was worth exploring.... > > > > Maybe also do a dev_warn() if there are missing > > > usb_autopm_put_interface() calls pending on close() ? > > > > > > > This way: > > > > - we do not have an artificial delay that might not work for all the use cases > > > > - cameras with noncompliant async controls will have the same PM > > > > behaviour as now (will be powered on until close() ) > > > > > > > > We do the same with the rest of the actions that require hardware access, like: > > > > https://lore.kernel.org/linux-media/20220920-resend-powersave-v5-2-692e6df6c1e2@xxxxxxxxxxxx/ > > > > > > > > This way: > > > > - Apps that do not need to access the hardware, do not wake it up, and > > > > we do not break usecases. > > > > > > > > Next steps will be: > > > > - cache the formats > > > > - move the actual set_ctrl to streamon... but if we can do that I > > > > would argue than we can move completely to the control framework. > > > > > > Right I had forgotten that the UVC driver does not use the control > > > framework. I think moving to that would be a prerequisite for moving > > > the set_ctrl to stream_on. > > -- > Regards, > > Laurent Pinchart -- Ricardo Ribalda
