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

Tomasz Figa tfiga at chromium.org
Wed Jul 22 20:10:03 CEST 2020 

On Wed, Jul 22, 2020 at 7:56 PM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> 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 ?
>

Yes, it's a recent change for a new platform where we ended up with
dynamic detection of components. Actually it hasn't landed yet. The CL
for reference is
https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2239080.

> > > 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

More information about the libcamera-devel mailing list