Re: [Xen-devel] [PATCH v5 1/1] cameraif: add ABI for para-virtual camera

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

On 3/12/19 10:58 AM, Hans Verkuil wrote:
> Hi Oleksandr,
>
> Just one comment:
>
> On 3/12/19 9:20 AM, Oleksandr Andrushchenko wrote:
> > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> >
> > This is the ABI for the two halves of a para-virtualized
> > camera driver which extends Xen's reach multimedia capabilities even
> > farther enabling it for video conferencing, In-Vehicle Infotainment,
> > high definition maps etc.
> >
> > The initial goal is to support most needed functionality with the
> > final idea to make it possible to extend the protocol if need be:
> >
> > 1. Provide means for base virtual device configuration:
> >   - pixel formats
> >   - resolutions
> >   - frame rates
> > 2. Support basic camera controls:
> >   - contrast
> >   - brightness
> >   - hue
> >   - saturation
> > 3. Support streaming control
> >
> > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > ---
> >   xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
> >   1 file changed, 1370 insertions(+)
> >   create mode 100644 xen/include/public/io/cameraif.h
> >
> > diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
> > new file mode 100644
> > index 000000000000..1ae4c51ea758
> > --- /dev/null
> > +++ b/xen/include/public/io/cameraif.h
> > @@ -0,0 +1,1370 @@
> <snip>
>
> > +/*
> > + * Request camera buffer's layout:
> > + *         0                1                 2               3        octet
> > + * +----------------+----------------+----------------+----------------+
> > + * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
> > + * +----------------+----------------+----------------+----------------+
> > + * |                             reserved                              | 8
> > + * +----------------+----------------+----------------+----------------+
> > + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> > + * +----------------+----------------+----------------+----------------+
> > + * |                             reserved                              | 64
> > + * +----------------+----------------+----------------+----------------+
> > + *
> > + * See response format for this request.
> > + *
> > + *
> > + * Request number of buffers to be used:
> > + *         0                1                 2               3        octet
> > + * +----------------+----------------+----------------+----------------+
> > + * |               id                | _OP_BUF_REQUEST|   reserved     | 4
> > + * +----------------+----------------+----------------+----------------+
> > + * |                             reserved                              | 8
> > + * +----------------+----------------+----------------+----------------+
> > + * |    num_bufs    |                     reserved                     | 12
> > + * +----------------+----------------+----------------+----------------+
> > + * |                             reserved                              | 16
> > + * +----------------+----------------+----------------+----------------+
> > + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> > + * +----------------+----------------+----------------+----------------+
> > + * |                             reserved                              | 64
> > + * +----------------+----------------+----------------+----------------+
> > + *
> > + * num_bufs - uint8_t, desired number of buffers to be used.
> > + *
> > + * If num_bufs is not zero then the backend validates the requested number of
> > + * buffers and responds with the number of buffers allowed for this frontend.
> > + * Frontend is responsible for checking the corresponding response in order to
> > + * see if the values reported back by the backend do match the desired ones
> > + * and can be accepted.
> > + * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
> > + * before sending XENCAMERA_OP_STREAM_START request to update or tune the
> > + * final configuration.
> > + * Frontend is not allowed to change the number of buffers and/or camera
> > + * configuration after the streaming has started.
> This last sentence isn't quite right, and I missed that when reviewing the
> proposed text during the v4 discussions.
>
> The bit about not being allowed to change the number of buffers when streaming
> has started is correct.
>
> But the camera configuration is more strict: you can't change the camera
> configuration after this request unless you call this again with num_bufs = 0.
>
> The camera configuration changes the buffer size, so once the buffers are
> allocated you can no longer change the camera config. It is unrelated to 
> streaming.
Can you please give me a hint of what would be the right thing to put in?

Thank you,
Oleksandr
> Regards,
>
>         Hans
>
> > + *
> > + * If num_bufs is 0 and streaming has not started yet, then the backend will
> > + * free all previously allocated buffers (if any).
> > + * Trying to call this if streaming is in progress will result in an error.
> > + *
> > + * If camera reconfiguration is required then the streaming must be stopped
> > + * and this request must be sent with num_bufs set to zero and finally
> > + * buffers destroyed.
> > + *
> > + * Please note, that the number of buffers in this request must not exceed
> > + * the value configured in XenStore.max-buffers.
> > + *
> > + * See response format for this request.
> > + */
> <snip>
>
> Regards,
>
>         Hans

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