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

[Kieran Bingham]

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.

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