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

[Laurent Pinchart]

Hi Tomasz,

On Wed, Jul 22, 2020 at 04:31:42PM +0200, Tomasz Figa wrote:
> On Wed, Jul 22, 2020 at 4:19 PM Kieran Bingham 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.

Has it always worked like that, or is it fairly recent ? If the service
is restarted when new devices appear, everything should be fine even if
the HAL initializes successfully with zero cameras, shouldn't it ?

> > 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,

Laurent Pinchart