[PATCHv2] usb/gadget/uvc-configs Fix host unable to negotiate framesizes other than first

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Joel,

(CC'ing Paul Elder who is working on the UVC gadget driver)

Thank you for the patch.

On Monday, 19 March 2018 21:36:41 EET Joel Pepper wrote:
> Add bFrameIndex as a UVCG_FRAME_ATTR for each frame size.
> Before all "bFrameindex" attributes were set to "1" with no way to
> configure the gadget otherwise. This resulted in the host always
> negotiating for bFrameIndex 1 (i.e. the first framesize of the gadget).
> After the negotiation the host driver will set the user or application
> selected framesize, while the gadget is actually set to the first
> framesize.
> 
> Note that this still requires the gadget to be configured with unique
> bFrameIndexes for each frameSize of each format through configfs. An
> alternative might be to automatically assign ascending indices when the
> format is linked into the streaming header, but the user space gadget
> would need a way to check or predict the indices so that it can properly
> interpret to PROBE/COMMIT CONTROL requests

It would indeed be nice if the indices could be automatically generated, to 
avoid giving userspace another possibility to create invalid descriptors. As 
you've correctly noted, that would require a way for the userspace helper 
application to coordinate with the UVC gadget driver. Would it be difficult to 
do so by defining the bFrameIndex attribute as read-only ? There's the 
additional issue of finding a place to store the index counter locally to the 
format, I'm not sure how that's done with the configfs API, but if it's not 
too difficult I think it would be a good option.

> v2: Add the new attribute to both MJPEG and uncompressedframe descriptos
> in Documentation/ABI, with note that it was added only in a later
> kernel version
> 
> Signed-off-by: Joel Pepper <joel.pepper@rwth-aachen.de>
> ---
>  Documentation/ABI/testing/configfs-usb-gadget-uvc | 17 +++++++++++++++++
>  drivers/usb/gadget/function/uvc_configfs.c        |  3 +++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/configfs-usb-gadget-uvc
> b/Documentation/ABI/testing/configfs-usb-gadget-uvc index 1ba0d0f..d435cf7
> 100644
> --- a/Documentation/ABI/testing/configfs-usb-gadget-uvc
> +++ b/Documentation/ABI/testing/configfs-usb-gadget-uvc
> @@ -194,6 +194,14 @@ Description:	Specific MJPEG frame descriptors
>  		bmCapabilities		- still image support, fixed frame-rate
>  					support
> 
> +Date:		Mar 2018
> +KernelVersion:	4.16
> +
> +		bFrameIndex		- unique id for this framedescriptor;
> +					if using multiple framedescriptors for
> +					same format, user needs to set distinct
> +					value for each frame descriptor
> +
>  What:		/config/usb-gadget/gadget/functions/uvc.name/streaming/
uncompressed
>  Date:		Dec 2014
>  KernelVersion:	4.0
> @@ -241,6 +249,15 @@ Description:	Specific uncompressed frame descriptors
>  		bmCapabilities		- still image support, fixed frame-rate
>  					support
> 
> +Date:           Mar 2018
> +KernelVersion:  4.16
> +
> +                bFrameIndex             - unique id for this
> framedescriptor; +                                        if using multiple
> framedescriptors for +                                        same format,
> user needs to set distinct +                                        value
> for each frame descriptor +
> +
>  What:		/config/usb-gadget/gadget/functions/uvc.name/streaming/header
>  Date:		Dec 2014
>  KernelVersion:	4.0
> diff --git a/drivers/usb/gadget/function/uvc_configfs.c
> b/drivers/usb/gadget/function/uvc_configfs.c index c9b8cc4a..5966d65 100644
> --- a/drivers/usb/gadget/function/uvc_configfs.c
> +++ b/drivers/usb/gadget/function/uvc_configfs.c
> @@ -992,6 +992,8 @@ UVC_ATTR(uvcg_frame_, cname, aname);
> 
>  UVCG_FRAME_ATTR(bm_capabilities, bmCapabilities, noop_conversion,
>  		noop_conversion, 8);
> +UVCG_FRAME_ATTR(b_frame_index, bFrameIndex, noop_conversion,
> +		noop_conversion, 8);
>  UVCG_FRAME_ATTR(w_width, wWidth, le16_to_cpu, cpu_to_le16, 16);
>  UVCG_FRAME_ATTR(w_height, wHeight, le16_to_cpu, cpu_to_le16, 16);
>  UVCG_FRAME_ATTR(dw_min_bit_rate, dwMinBitRate, le32_to_cpu, cpu_to_le32,
> 32);
> @@ -1137,6 +1139,7 @@ UVC_ATTR(uvcg_frame_, dw_frame_interval,
> dwFrameInterval);
> 
>  static struct configfs_attribute *uvcg_frame_attrs[] = {
>  	&uvcg_frame_attr_bm_capabilities,
> +	&uvcg_frame_attr_b_frame_index,
>  	&uvcg_frame_attr_w_width,
>  	&uvcg_frame_attr_w_height,
>  	&uvcg_frame_attr_dw_min_bit_rate,