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.
--
Regards,
Laurent Pinchart
