[libcamera-devel] [PATCH] android: camera_hal_manager: Fail on no cameras

[Tomasz Figa]

On Wed, Jul 22, 2020 at 4:19 PM Kieran Bingham
<kieran.bingham at ideasonboard.com> wrote:
>
> Hi Laurent, Jacopo,
>
> Jacopo, I'm sorry for the noise, it seems my opinions were based on an
> invalid assumption about what is reasonable :-( and a lack of
> understanding of how CrOS implemented working around that assumption.
>
> So my whole premise has been completely wrong and should be ignored.
>
>
> On 22/07/2020 14:49, Laurent Pinchart wrote:
> > Hello,
> >
> > (CC'ing Tomasz)
> >
> > On Wed, Jul 22, 2020 at 12:24:56PM +0100, Kieran Bingham wrote:
> >> On 22/07/2020 12:12, Jacopo Mondi wrote:
> >>> Hi Kieran,
> >>>    I think the conversation diverged, as I was clearly overlooking
> >>> the UVC camera use case and you're missing the intended use case of
> >>> this patch. I'll try to reply and summarize at the end.
> >>
> >> My interpretation is that this patch fixes the issue you are
> >> experiencing, (which is a valid thing to do, and this is likely a
> >> suitable solution for the time being)
> >>
> >> I was indeed trying to highlight that it would cause breakage for the
> >> UVC style use cases, and I believe system degradation for systems with
> >> no cameras attached, and which is why I thought a \todo is required.
> >>
> >>> On Tue, Jul 21, 2020 at 09:59:10PM +0100, Kieran Bingham wrote:
> >>>> On 21/07/2020 14:09, Jacopo Mondi wrote:
> >>>>> On Tue, Jul 21, 2020 at 01:47:29PM +0100, Kieran Bingham wrote:
> >>>>>> Hi Jacopo,
> >>>>>>
> >>>>>> On 21/07/2020 13:13, Jacopo Mondi wrote:
> >>>>>>> Hi Kieran,
> >>>>>>>
> >>>>>>> On Tue, Jul 21, 2020 at 12:41:16PM +0100, Kieran Bingham wrote:
> >>>>>>>> Hi Jacopo,
> >>>>>>>>
> >>>>>>>> On 21/07/2020 12:26, Jacopo Mondi wrote:
> >>>>>>>>> The CameraHalManager initialization tries to start the
> >>>>>>>>> libcamera::CameraManager which enumerate the registered cameras.
> >>>>>>>>>
> >>>>>>>>> When initialization is called too early during system boot, it might
> >>>>>>>>> happen that the media graphs are still being registered to user-space
> >>>>>>>>> preventing any pipeline handler to match and register cameras.
> >>>>>>>>>
> >>>>>>>>> If that happens, the CameraHalManager silently accepts that no
> >>>>>>>>> cameras are available in the system, reporting that information
> >>>>>>>>> to the camera stack:
> >>>>>>>>>
> >>>>>>>>> cros_camera_service[2054]: (5) StartOnThread(): Camera module "libcamera camera HALv3 module" has 0 built-in camera(s)
> >>>>>>>>> cros_camera_service[2054]: (5) StartOnThread(): SuperHAL started with 1 modules and 0 built-in cameras
> >>>>>>>>> CameraProviderManager: Camera provider legacy/0 ready with 0 camera devices
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>> Hrm ... should this be part of the hotplug work that as cameras become
> >>>>>>>> available this gets updated somehow? - Even on *non* hotpluggable pipelines?
> >>>>>>>>
> >>>>>>>
> >>>>>>> I don't get what your comment is about here, I'm sorry
> >>>>>>
> >>>>>>
> >>>>>> Your patch prevents loading of libcamera completely unless there is at
> >>>>>> least one camera right ?
> >>>>>>
> >>>>>> What happens on say an x86 platform which will only have UVC cameras,
> >>>>>> yet will use libcamera...
> >>>>>>
> >>>>>> When will it be acceptable to load the camera service.
> >>>>>>
> >>>>>> Should the service itself continually fail, and respawn until someone
> >>>>>> plugs in a camera?
> >>>>>>
> >>>>>
> >>>>> That's my understanding
> >>>>
> >>>> That sounds like that would cause a very bad implementation to me.
> >>>>
> >>>> Waiting for upstart to decide when to retry launching the camera-service
> >>>> wouldn't be an acceptable time to wait IMO.
> >>>>
> >>>> Either it tries every second, and is flooding the system, or it tries
> >>>> every minute and it takes a minute before you can view your newly
> >>>> attached UVC camera ...
> >>>>
> >>>> I would expect event driven camera attachment, not polled ...
> >>>
> >>> For UVC we will have to register non-active cameras and notify to
> >>> android they're available when hotplug is detected
> >>
> >> Yes, this is what I think I see that the platform2/camera/hal/usb*
> >> implementation does in CrOS.
> >>
> >>> For non-pluggable cameras, as shall wait until the pipeline handler is
> >>> matched and has registered cameras
> >>
> >> The issue for us is that *we support UVC* ... so we're now a UVC capable
> >> stack.
> >>
> >> I believe that means we will in some form or another have to also do the
> >> same (some sort of pre-allocation if that's what is needed to make
> >> android happy). I dislike the idea that we would then have a 'maximum
> >> supported cameras' but maybe it is set arbitrarily high so it doesn't
> >> get hit without an extreme use case.
> >
> > I don't think we can do this, as, as far as I know, Android doesn't
> > support status changes for internal cameras. Only cameras reported as
> > external can generate a status change event. Quoting from
> > camera/provider/2.4/ICameraProviderCallback.hal in
> > https://android.googlesource.com/platform/hardware/interfaces:
> >
> >      * On camera service startup, when ICameraProvider::setCallback is invoked,
> >      * the camera service must assume that all internal camera devices are in
> >      * the CAMERA_DEVICE_STATUS_PRESENT state.
> >      *
> >      * The provider must call this method to inform the camera service of any
> >      * initially NOT_PRESENT devices, and of any external camera devices that
> >      * are already present, as soon as the callbacks are available through
> >      * setCallback.
> >
> >> Now ... given that we (if we support UVC) must support dynamically
> >> adding cameras when they are available - I anticipate that the hotplug
> >> work will do that.
> >>
> >> When we do that, We could also use it for -non hotplug cameras, and
> >> simply allow cameras to be registered correctly using the same methods
> >> as they are discovered/notified by udev/hotplug mechanisms.
> >>
> >> Because even if they are fixed CSI2 busses, we're still going to get
> >> udev events when they appear as a media-device right ?
> >
> > Yes, on the libcamera side hotplug should work perfectly fine for
> > internal cameras, but unfortunately not on the Android side.
> >
> >>>>>> So taking that further, what I'm saying is, perhaps this should be
> >>>>>> perfectly able to launch with zero cameras, and /when/ cameras are
> >>>>>> created they should notify android that a new camera is now available.
> >>>>>
> >>>>> Do you know if that's even possible ?
> >>>>>
> >>>>> I think Android expects the number of possible cameras to be
> >>>>> statically defined, there's a callback to notify a change of status of
> >>>>> a device, but we're dealing here with -creating- cameras based on the
> >>>>> number of cameras detected by android.
> >>>>
> >>>> So, looking at the USB HAL in cros - it does look like they pre-allocate
> >>>> some cameras or such and only activate them on device connection.
> >>>>
> >>>> I fear we might have to do the same somehow in the future, as indeed it
> >>>> might not be possible to tell android there is a 'new' camera. Only an
> >>>> update to an existing one... not sure it will require more investigation.
> >>>
> >>> Yes, but that's for UVC. Built-in cameras are different, and Android
> >>> bets on the fact if you have a camera service running then your system
> >>> has cameras which are expected to be registered.
> >>>
> >>> Keep in mind so far there's been an HAL for UVC and one for built-in
> >>> cameras. We're handling both and that's a new use case afaict
> >>
> >> Precisely - and that's what I've been trying to discuss on this patch
> >> ;-) I'm sorry my thoughts didn't come across clearly.
> >>
> >>>>>>>>> Fix this by returning an error code if no camera is registered in the
> >>>>>>>>> system at the time CameraHalManager::init() is called. The camera
> >>>>>>>>> framework then tries to re-load the HAL module later in time, hopefully
> >>>>>>>>> after the media device dependencies have been registered:
> >>>>>>>>>
> >>>>>>>>> 2020-07-21T12:26:37.903456+02:00 INFO cros_camera_service[2054]: (5) StartOnThread(): Camera module "libcamera camera HALv3 module" has 0 built-in camera(s)
> >>>>>>>>> 2020-07-21T12:26:37.903521+02:00 INFO cros_camera_service[2054]: (5) StartOnThread(): SuperHAL started with 1 modules and 0 built-in cameras
> >>>>>>>>> ....
> >>>>>>>>> 2020-07-21T12:30:36.662877+02:00 INFO cros_camera_service[5908]: (5910) StartOnThread(): Camera module "libcamera camera HALv3 module" has 2 built-in camera(s)
> >>>>>>>>> 2020-07-21T12:30:36.663196+02:00 INFO cros_camera_service[5908]: (5910) StartOnThread(): SuperHAL started with 1 modules and 2 built-in cameras
> >>>>>>>>>
> >>>>>>>>> Return -ENODEV as according to camera_common.h specification is the
> >>>>>>>>> only supported error code. The CrOS HAL adapter does not distinguish
> >>>>>>>>> between that and other negative values, so it does not really make
> >>>>>>>>> a difference.
> >>>>>>>>
> >>>>>>>> This feels a bit punchy/racey still. And what happens in the instance
> >>>>>>>> that we really don't yet have any cameras? (I.e. a UVC only platform,
> >>>>>>>> which doesn't yet have any cameras connected).
> >>>>>>>
> >>>>>>> You keep defferring ? I think the framework handles that
> >>>>>>
> >>>>>> I would be surprised if it would be expected behaviour to just poll
> >>>>>> launching of the camera service until there is a camera there to satisfy
> >>>>>> it ...
> >
> > This is actually how the camera HALs in Chrome OS handle this issue :-(
>
>
> Oh dear :-( Well I guess that invalidates all my assumptions
>
> /me throws toys out of the pram.
>
>
> >>>>>>>> How many times will we defer? How long does it defer for for instance?
> >>>>>>>
> >>>>>>> Usually 1 is enough from my testing. I don't think we have to care
> >>>>>>> what is the timeout in the framework, as afaict android services are
> >>>>>>> restarted by default.
> >>>>>>
> >>>>>> Ok, so this is mostly dealing with the race at startup ...
> >>>>>>
> >>>>>>>>> Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> >>>>>>>>> ---
> >>>>>>>>>  src/android/camera_hal_manager.cpp | 11 +++++++++++
> >>>>>>>>>  1 file changed, 11 insertions(+)
> >>>>>>>>>
> >>>>>>>>> diff --git a/src/android/camera_hal_manager.cpp b/src/android/camera_hal_manager.cpp
> >>>>>>>>> index 02b6418fb36d..e967d210e547 100644
> >>>>>>>>> --- a/src/android/camera_hal_manager.cpp
> >>>>>>>>> +++ b/src/android/camera_hal_manager.cpp
> >>>>>>>>> @@ -73,6 +73,17 @@ int CameraHalManager::init()
> >>>>>>>>>               ++index;
> >>>>>>>>>       }
> >>>>>>>>>
> >>>>>>>>> +     /*
> >>>>>>>>> +      * If no pipeline has registered cameras, defer initialization to give
> >>>>>>>>> +      * time to media devices to register to user-space.
> >>>>>>>>> +      */
> >>>>>>>>> +     if (index == 0) {
> >>>>>>>>> +             LOG(HAL, Debug) << "Defer CameraHALManager initialization";
> >>>>>>>>
> >>>>>>>> I think perhaps this needs a higher level than Debug to make sure it
> >>>>>>>> always prints somewhere.
> >>>>>>>
> >>>>>>> I think that's kind of expected to happen, I don't think this should
> >>>>>>> be an error
> >>>>>>
> >>>>>> Info? Warning?
> >>>>>>
> >>>>>> If libcamera has prevented loading, I think it would be good to know
> >>>>>> about it by default...
> >>>>>>
> >>>>>>>> I fear this will be deflecting the issue, and introduces races (i.e.
> >>>>>>>> this would go through if only one camera of two in the system is available).
> >>>>>>>
> >>>>>>> If the pipeline handler match (ie the device enumerator matches the
> >>>>>>> dependencies) than the match() function continues and register
> >>>>>>> cameras. I don't think we can found ourselves in a semi-initialized
> >>>>>>> state.
> >>>>>>
> >>>>>> Ok, so it really is about having at least one camera available?
> >>>>>
> >>>>> It's about at least a pipeline being matched.
> >>>>
> >>>> Ok, but I don't think it's that difficult to conjur up a scenario where
> >>>> there won't be a device
> >>>
> >>> Not for what Android has been thought to work on. You integrate a
> >>> system with cameras, it's fair to defer until those cameras are
> >>> registered. You have no cameras, either you disable the camera stack
> >>> or you register 0 cameras and then the camera subsystem is silent and
> >>> not accessible.
> >>
> >> Android is wrong - It should always support UVC hotplug ;-) hehehe.
> >>
> >> I've been annoyed I haven't been able to connect a UVC camera to my
> >> phone before ;-)
> >>
> >>>>>> I think looking at CameraHalManager::init(), as it only creates a
> >>>>>> CameraDevice for cameras available in cameraManager_->cameras(), it
> >>>>>> /could/ be a race, it's just that creating two cameras is fast, so we're
> >>>>>> unlikely to get in here between the point that one has been available
> >>>>>> and another is still loading ...
> >>>>>
> >>>>> I don't think that's possible.
> >>>>>
> >>>>> If a all the dependencies of a pipeline handler are matched, the
> >>>>> camera are registered. What is the code flow that registers one
> >>>>> camera, returns to the camera manager, then calls the pipeline handler
> >>>>> again to register more ?
> >>>>
> >>>> At least PipelineHandlerUVC will call PipelineHandler::match() once for
> >>>> each camera attached.
> >>>>
> >>>> But yes, perhaps due to the threading model, it won't be a possible race.
> >>>>
> >>>> I was thinking of when a pipeline starts and only 'one' of it's media
> >>>> devices is available.
> >>>
> >>> Yes, for UVC that's different I agree. A call to
> >>> CameraManager::start() might match one uvc media device but miss a
> >>> second one which still have to appear to userspace.
> >>>
> >>> As said, UVC needs some special handling and pre-register cameras
> >>
> >> Yes, and we will therefore /have/ to do that.
> >
> > I also don't see any way around this *for UVC*.
> >
> >>>>>> But still ... I think this is stuff that will get dealt with by hotplug
> >>>>>> being added to the HAL.
> >>>>>
> >>>>> I agree, we should support inserting and removing new cameras, but I
> >>>>> think at this point, we should really start only if cameras are
> >>>>> registered and any pipeline handler is matched.
> >>>>>
> >>>>> I'm not sure I got what other alternative approach you are proposing
> >>>>> to be honest.
> >>>>
> >>>> I'm suggesting that when hotplug support is available, this patch, if
> >>>> integrated, might need to be reverted in effect ... and thus a todo note
> >>>> should be added to say that or such.
> >>>>
> >>>> I believe we should be able to start the camera service successfully
> >>>> with zero cameras if there are zero cameras at the time the service starts.
> >>>
> >>> I don't think so for built-in cameras. We start the service when
> >>> cameras are registered, otherwise if you have to pre-allocate cameras
> >>> you would need to know how many of them the pipeline handler expects
> >>> to register and that's not known before it has been matched.
> >>
> >> Yes, not knowing in advance is a pain point.
> >>
> >>> UVC, again, is a different story as it supports hotplug.
> >>
> >> But equally we don't know how many UVC cameras someone could connect,
> >> but we can define a max. The question would then be if that 'max'
> >> includes static cameras, as well as dynamic UVC cameras, or if it's 'on
> >> top' of the static cameras.
> >>
> >> Including it in the max, means we can just preallocate the camera
> >> registrations for Android sake, and register the (static) cameras in
> >> that list as soon as they are available through the udev notifications
> >> system.
> >>
> >>>>>>>> ..
> >>>>>>>>
> >>>>>>>> Perhaps it can still go in if it solves an immediate problem, but in
> >>>>>>>> that case I think it needs a \todo or a warning of some kind...
> >>>>>>>
> >>>>>>> A \todo item to record this should be fixed how ?
> >>>>>>>
> >>>>>>> Unless we expect the CameraManager to stall until any of the pipeline
> >>>>>>> handler it tries match, but this seems not a good idea to me.
> >>>>>>
> >>>>>> No, i don't expect it to stall ... I expect it to complete successfully,
> >>>>>> and if there are only 0 cameras, it will only have zero cameras - until
> >>>>>
> >>>>> That means Android/CrOS starts without the camera being active (ie.
> >>>>> the camera application icon is not available, in CrOS in example).
> >>>>
> >>>> Hrm, so it disables the app completely?
> >>>>
> >>>> Anyway, essentially I'm thinking - whatever happens with the existing
> >>>> UVC stack is what we would need to be able to mirror.
> >>>>
> >>>>>> they become available at which point they'll be registered through the
> >>>>>> same mechanisms as the hotplugging ...
> >>>>>
> >>>>> Still I don't get if you are talking about libcamera hotplug or
> >>>>> android hotplug, which, to my understanding, expects anyway a camera
> >>>>> device to be registered but marked as 'not present' (looking at the
> >>>>> camera_device_status enumeration)
> >>>>
> >>>>
> >>>> I was going to ask how does it register camera's it doesn't know will
> >>>> exist, but I think I saw that the UVC HAL just pre-allocates some
> >>>> cameras or such, so that explains how that one works.
> >>>>
> >>>
> >>> I see three cases:
> >>> 1) No uvc support
> >>>    Defer until a pipeline handler is matched and has registered
> >>>    cameras
> >>>
> >>> 2) UVC only
> >>>    Need to pre-register cameras and activate on hot-plug. Knowing when
> >>>    this has to happen is tricky, as the HAL needs to know it should
> >>>    not wait for built-in cameras and can proceed to register
> >>>    non-active USB cameras
> >>>
> >>> 3) built-in + UVC
> >>>    Simmilarly, knowing we have to wait for built-in to appear, we
> >>>    defer until cameras are available, then pre-register UVC cameras.
> >>>
> >>> The hard part I think it is to define how to instruct the HAL it has
> >>> to wait for built-in to appear or not before registering UVC
> >>> non-active cameras.
> >>
> >> My suggestion is (not blocking this patch, but on top) to do so by
> >> treating static cameras and hotpluggable cameras in the same way.
> >>
> >> It's just that static cameras will never 'unplug' (unless someone
> >> unbinds them? but we all know how bad that mess would get with V4L2 anyway)
> >
> > As explained above, this is unfortunately not an option. To make this
> > matter more complicated, we need to wait for *all* built-in cameras to
> > be available before initializing, as otherwise the system will be
> > permanently stuck with only part of the cameras available.
> >
> > I think this isn't something we should solve, the system should ensure
> > that device nodes have been created before starting the camera service.
>
> Yes, given what you've clarified, then I agree - the service should be
> dependent upon the devices being brought up. I think systemd can do
> that, but CrOS uses upstart, so I don't know what that might support.

As ugly as it sounds, we have an udev rule which restarts the camera
service when devices matching the internal cameras show up. I believe
we match them by the "video4linux" class and particular hardware
subsystems, e.g. PCI or I2C.

>
> But that's out of scope (and control) for us I think ...
>
>
> > I've expressed this before in a conversation with Tomasz (not sure if it
> > was on the public mailing list, IRC, or in private), but we didn't reach
> > an agreement at the time. One option that was discussed was a platform
> > configuration file that would list the cameras expected to be present (I
> > think everybody knows how much I like that :-)). Another option that has
> > been experimented was
> > https://lists.libcamera.org/pipermail/libcamera-devel/2019-September/004850.html.
>
>
> --
> Regards
> --
> Kieran