Re: Devices with a front and back webcam represented as a single UVC device

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11-07-18 20:26, Carlos Garnacho wrote:
> Hi!,
> 
> On Wed, Jul 11, 2018 at 7:41 PM, Hans de Goede <hdegoede@redhat.com> wrote:
>> Hi,
>>
>>
>> On 11-07-18 18:07, Carlos Garnacho wrote:
>>>
>>> Hi!,
>>>
>>> On Wed, Jul 11, 2018 at 2:41 PM, Hans de Goede <hdegoede@redhat.com>
>>> wrote:
>>>>
>>>> HI,
>>>>
>>>>
>>>> On 11-07-18 14:08, Laurent Pinchart wrote:
>>>>>
>>>>>
>>>>> Hi Carlos,
>>>>>
>>>>> On Wednesday, 11 July 2018 14:36:48 EEST Carlos Garnacho wrote:
>>>>>>
>>>>>>
>>>>>> On Wed, Jul 11, 2018 at 1:00 PM, Laurent Pinchart wrote:
>>>>>>>
>>>>>>>
>>>>>>> On Wednesday, 11 July 2018 11:37:14 EEST Hans de Goede wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> Hi Laurent,
>>>>>>>>
>>>>>>>> At Guadec Carlos (in the Cc) told me that on his Acer 2-in-1 only
>>>>>>>> the frontcam is working and it seems both are represented by a
>>>>>>>> single UVC USB device. I've told him to check for some v4l control
>>>>>>>> to flip between front and back.
>>>>>>>>
>>>>>>>> Carlos, as I mentioned you can try gtk-v4l
>>>>>>>> ("sudo dnf install gtk-v4l") or qv4l2
>>>>>>>> ("sudo dnf install qv4l2") these will both show
>>>>>>>> you various controls for the camera. One of those might do the trick.
>>>>>>>>
>>>>>>>> But I recently bought a 2nd second hand Cherry Trail based HP
>>>>>>>> X2 2-in-1 and much to my surprise that is actually using an UVC
>>>>>>>> cam, rather then the usual ATOMISP crap and it has the same issue.
>>>>>>>>
>>>>>>>> This device does not seem to have a control to flip between the
>>>>>>>> 2 cams, instead it registers 2 /dev/video? nodes but the second
>>>>>>>> node does not work
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> The second node is there to expose metadata to userspace, not image
>>>>>>> data.
>>>>>>> That's a recent addition to the uvcvideo driver.
>>>>>>>
>>>>>>>> and dmesg contains:
>>>>>>>>
>>>>>>>> [   26.079868] uvcvideo: Found UVC 1.00 device HP TrueVision HD
>>>>>>>> (05c8:03a3)
>>>>>>>> [   26.095485] uvcvideo 1-4.2:1.0: Entity type for entity Extension 4
>>>>>>>> was
>>>>>>>> not initialized!
>>>>>>>> [   26.095492] uvcvideo 1-4.2:1.0: Entity type for entity Processing
>>>>>>>> 2
>>>>>>>> was
>>>>>>>> not initialized!
>>>>>>>> [   26.095496] uvcvideo 1-4.2:1.0: Entity type for entity Camera 1
>>>>>>>> was
>>>>>>>> not
>>>>>>>> initialized!
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> You can safely ignore those messages. I need to submit a patch to get
>>>>>>> rid
>>>>>>> of them.
>>>>>>>
>>>>>>>> Laurent, I've attached lsusb -v output so that you can check the
>>>>>>>> descriptors.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Thank you.
>>>>>>>
>>>>>>> It's funny how UVC specifies a standard way to describe a device with
>>>>>>> two
>>>>>>> camera sensors with dynamic selection of one of them at runtime, and
>>>>>>> vendors instead implement vendor-specific crap :-(
>>>>>>>
>>>>>>> The interesting part in the descriptors is
>>>>>>>
>>>>>>>          VideoControl Interface Descriptor:
>>>>>>>            bLength                27
>>>>>>>            bDescriptorType        36
>>>>>>>            bDescriptorSubtype      6 (EXTENSION_UNIT)
>>>>>>>            bUnitID                 4
>>>>>>>            guidExtensionCode
>>>>>>> {1229a78c-47b4-4094-b0ce-db07386fb938}
>>>>>>>            bNumControl             2
>>>>>>>            bNrPins                 1
>>>>>>>            baSourceID( 0)          2
>>>>>>>            bControlSize            2
>>>>>>>            bmControls( 0)       0x00
>>>>>>>            bmControls( 1)       0x06
>>>>>>>            iExtension              0
>>>>>>>
>>>>>>> The extension unit exposes two controls (bmControls is a bitmask).
>>>>>>> They
>>>>>>> can be accessed from userspace through the UVCIOC_CTRL_QUERY ioctl, or
>>>>>>> mapped to V4L2 controls through the UVCIOC_CTRL_MAP ioctl, in which
>>>>>>> case
>>>>>>> they will be exposed to standard V4L2 applications.
>>>>>>>
>>>>>>> If you want to experiment with this, I would advise querying both
>>>>>>> controls
>>>>>>> with UVCIOC_CTRL_QUERY. You can use the UVC_GET_CUR, UVC_GET_MIN,
>>>>>>> UVC_GET_MAX, UVC_GET_DEF and UVC_GET_RES requests to get the control
>>>>>>> current, minimum, maximum, default and resolution values, and
>>>>>>> UVC_GET_LEN
>>>>>>> and UVC_GET_INFO to get the control size (in bytes) and flags. Based
>>>>>>> on
>>>>>>> that you can start experimenting with UVC_SET_CUR to set semi-random
>>>>>>> values.
>>>>>>>
>>>>>>> I'm however worried that those two controls would be a register
>>>>>>> address
>>>>>>> and a register value, for indirect access to all hardware registers in
>>>>>>> the device. In that case, you would likely need information from the
>>>>>>> device vendor, or possibly a USB traffic dump from a Windows machine
>>>>>>> when
>>>>>>> switching between the front and back cameras.
>>>>>>>
>>>>>>>> Carlos, it might be good to get Laurent your descriptors too, to do
>>>>>>>> this do "lsusb", note what is the <vid>:<pid> for your camera and
>>>>>>>> then
>>>>>>>> run:
>>>>>>>>
>>>>>>>> sudo lsusb -v -d <vid>:<pid>  > lsusb.log
>>>>>>>>
>>>>>>>> And send Laurent a mail with the generated lsusb
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> That would be appreciated, but I expect the same issue :-(
>>>>>>
>>>>>>
>>>>>>
>>>>>> Please find it attached. IIUC your last email, it might not be the
>>>>>> exact same issue, but you can definitely judge better.
>>>>>
>>>>>
>>>>>
>>>>> Your device is similar in the sense that it doesn't use the standard UVC
>>>>> support for multiple camera sensors. It instead exposes two extension
>>>>> units:
>>>>>
>>>>>          VideoControl Interface Descriptor:
>>>>>            bLength                27
>>>>>            bDescriptorType        36
>>>>>            bDescriptorSubtype      6 (EXTENSION_UNIT)
>>>>>            bUnitID                 4
>>>>>            guidExtensionCode
>>>>> {1229a78c-47b4-4094-b0ce-db07386fb938}
>>>>>            bNumControl             2
>>>>>            bNrPins                 1
>>>>>            baSourceID( 0)          2
>>>>>            bControlSize            2
>>>>>            bmControls( 0)       0x00
>>>>>            bmControls( 1)       0x06
>>>>>            iExtension              0
>>>>>          VideoControl Interface Descriptor:
>>>>>            bLength                29
>>>>>            bDescriptorType        36
>>>>>            bDescriptorSubtype      6 (EXTENSION_UNIT)
>>>>>            bUnitID                 6
>>>>>            guidExtensionCode
>>>>> {26b8105a-0713-4870-979d-da79444bb68e}
>>>>>            bNumControl             9
>>>>>            bNrPins                 1
>>>>>            baSourceID( 0)          4
>>>>>            bControlSize            4
>>>>>            bmControls( 0)       0x1f
>>>>>            bmControls( 1)       0x01
>>>>>            bmControls( 2)       0x38
>>>>>            bmControls( 3)       0x00
>>>>>            iExtension              6 Realtek Extended Controls Unit
>>>>>
>>>>> The first one is identical to Hans', and I expect it to offer indirect
>>>>> access
>>>>> to internal device registers. The second one exposes 9 controls, and I
>>>>> expect
>>>>> at least some of those to have direct effects on the device. What they
>>>>> do
>>>>> and
>>>>> how they operate is unfortunately unknown.
>>>>
>>>>
>>>>
>>>> Laurent, thank you for your input on this. I thought it was a bit weird
>>>> that
>>>> the cam on my HP X2 only had what appears to be the debug controls, so I
>>>> opened it up and as I suspect (after your analysis) it is using a USB
>>>> module
>>>> for the front camera, but the back camera is a sensor directly hooked
>>>> with
>>>> its
>>>> CSI/MIPI bus to the PCB, so very likely it is using the ATOMISP stuff.
>>>>
>>>> So I think that we can consider this "solved" for my 2-in-1.
>>>>
>>>> Carlos, your Acer is using a Core CPU (not an Atom) right ? And the front
>>>
>>>
>>> Indeed, it is an i5...
>>>
>>>> and
>>>> rear cams are both centered at the same edge I guess ?  (mine had one in
>>>> the
>>>> corner and the other centered which already was a hint)
>>>
>>>
>>> ...but now that you mention this, I have front camera centered and
>>> rear camera on a corner too. Is there any other info I may need to
>>> fetch? I assume ATOMISP is irrelevant here.
>>
>>
>> Skylake and kabylake also have an ATOMISP like device. What is the
>> output of lspci ?  And what is your CPU model number? (cat /proc/cpuinfo)
> 
> Oh I see, this is Skylake indeed, so I guess the issue is similar.

I think that your CPU does have integrated camera support, but that does
not necessarily mean it is used. If it is used it should show up in
lspci.

Can you provide lspci output ?   And is there any output for:

lsmod | grep ipu3

Regards,

Hans