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

Laurent Pinchart laurent.pinchart at ideasonboard.com
Fri Jul 24 03:28:31 CEST 2020 

Hi Tomasz,

On Wed, Jul 22, 2020 at 08:10:03PM +0200, Tomasz Figa wrote:
> On Wed, Jul 22, 2020 at 7:56 PM Laurent Pinchart wrote:
> > 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.

Does this mean that if we integrate that change manually (including
possible dependencies), then no further action should be needed on the
HAL side ?

> >>> 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

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