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Message-ID: <20250714083414.GA8243@pendragon.ideasonboard.com>
Date: Mon, 14 Jul 2025 11:34:14 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Hans de Goede <hansg@...nel.org>, linux-media@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v8 5/5] media: uvcvideo: Auto-set UVC_QUIRK_MSXU_META
On Mon, Jul 14, 2025 at 10:21:20AM +0200, Ricardo Ribalda wrote:
> On Mon, 14 Jul 2025 at 10:06, Laurent Pinchart wrote:
> > On Mon, Jul 14, 2025 at 09:46:45AM +0200, Ricardo Ribalda wrote:
> > > On Fri, 11 Jul 2025 at 21:58, Laurent Pinchart wrote:
> > > > On Mon, Jul 07, 2025 at 06:34:05PM +0000, Ricardo Ribalda wrote:
> > > > > If the camera supports the MSXU_CONTROL_METADATA control, auto set the
> > > > > MSXU_META quirk.
> > > > >
> > > > > Reviewed-by: Hans de Goede <hansg@...nel.org>
> > > > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > > > ---
> > > > > drivers/media/usb/uvc/uvc_driver.c | 7 +++-
> > > > > drivers/media/usb/uvc/uvc_metadata.c | 75 +++++++++++++++++++++++++++++++++++-
> > > > > drivers/media/usb/uvc/uvcvideo.h | 2 +-
> > > > > include/linux/usb/uvc.h | 3 ++
> > > > > 4 files changed, 84 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > > > > index 56ea20eeb7b9d5d92f3d837c15bdf11d536e9f2d..9de5abb43e19d9e876cddc5d7124592953db89ac 100644
> > > > > --- a/drivers/media/usb/uvc/uvc_driver.c
> > > > > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > > > > @@ -2315,7 +2315,12 @@ static int uvc_probe(struct usb_interface *intf,
> > > > > goto error;
> > > > > }
> > > > >
> > > > > - uvc_meta_init(dev);
> > > > > + ret = uvc_meta_init(dev);
> > > > > + if (ret < 0) {
> > > > > + dev_err(&dev->udev->dev,
> > > > > + "Error initializing the metadata formats (%d)\n", ret);
> > > > > + goto error;
> > > > > + }
> > > > >
> > > > > if (dev->quirks & UVC_QUIRK_NO_RESET_RESUME)
> > > > > udev->quirks &= ~USB_QUIRK_RESET_RESUME;
> > > > > diff --git a/drivers/media/usb/uvc/uvc_metadata.c b/drivers/media/usb/uvc/uvc_metadata.c
> > > > > index 77e03273d3cf6b00cac6ebb9b29b941f1cbfd9f7..59bb133baf9a73ef6a30fa8ead85aa90653d60f4 100644
> > > > > --- a/drivers/media/usb/uvc/uvc_metadata.c
> > > > > +++ b/drivers/media/usb/uvc/uvc_metadata.c
> > > > > @@ -10,6 +10,7 @@
> > > > > #include <linux/list.h>
> > > > > #include <linux/module.h>
> > > > > #include <linux/usb.h>
> > > > > +#include <linux/usb/uvc.h>
> > > > > #include <linux/videodev2.h>
> > > > >
> > > > > #include <media/v4l2-ioctl.h>
> > > > > @@ -166,6 +167,71 @@ static const struct v4l2_file_operations uvc_meta_fops = {
> > > > > .mmap = vb2_fop_mmap,
> > > > > };
> > > > >
> > > > > +static struct uvc_entity *uvc_meta_find_msxu(struct uvc_device *dev)
> > > > > +{
> > > > > + static const u8 uvc_msxu_guid[16] = UVC_GUID_MSXU_1_5;
> > > > > + struct uvc_entity *entity;
> > > > > +
> > > > > + list_for_each_entry(entity, &dev->entities, list) {
> > > > > + if (!memcmp(entity->guid, uvc_msxu_guid, sizeof(entity->guid)))
> > > > > + return entity;
> > > > > + }
> > > > > +
> > > > > + return NULL;
> > > > > +}
> > > > > +
> > > > > +#define MSXU_CONTROL_METADATA 0x9
> > > > > +static int uvc_meta_detect_msxu(struct uvc_device *dev)
> > > > > +{
> > > > > + u32 *data __free(kfree) = NULL;
> > > > > + struct uvc_entity *entity;
> > > > > + int ret;
> > > > > +
> > > > > + entity = uvc_meta_find_msxu(dev);
> > > > > + if (!entity)
> > > > > + return 0;
> > > > > +
> > > > > + /*
> > > > > + * USB requires buffers aligned in a special way, simplest way is to
> > > > > + * make sure that query_ctrl will work is to kmalloc() them.
> > > > > + */
> > > > > + data = kmalloc(sizeof(*data), GFP_KERNEL);
> > > > > + if (!data)
> > > > > + return -ENOMEM;
> > > > > +
> > > > > + /* Check if the metadata is already enabled. */
> > > > > + ret = uvc_query_ctrl(dev, UVC_GET_CUR, entity->id, dev->intfnum,
> > > > > + MSXU_CONTROL_METADATA, data, sizeof(*data));
> > > > > + if (ret)
> > > > > + return 0;
> > > > > +
> > > > > + if (*data) {
> > > > > + dev->quirks |= UVC_QUIRK_MSXU_META;
> > > > > + return 0;
> > > > > + }
> > > > > +
> > > > > + /*
> > > > > + * We have seen devices that require 1 to enable the metadata, others
> > > > > + * requiring a value != 1 and others requiring a value >1. Luckily for
> > > >
> > > > I'm confused here. If those are three different behaviours, then value
> > > > != 1 would be value == 0 (as the third behaviour is value > 1). You test
> > > > for !*data below, so 0 is not accepted as a valid value for this
> > > > purpose. What am I missing ?
> > >
> > > There is a typo in the comment.
> > >
> > > Some devices require 1, some devices any value !=0, and other value=MAX.
> > > I will fix it in a follow-up patch.
> >
> > The documentation of the control states that MSXU_CONTROL_METADATA
> > reports the maximum size of the MS metadata generated by the device in
> > kB, and the control should be set to the value reported by GET_MAX to
> > enable metadata generation. That's what you're doing in this patch, so
> > you can update the comment to document there.
>
> Some vendors assumed the kB was a typo in MS spec and used bytes instead :)
> In this favor I must say that kB here sounds like a mistake, I haven't
> seen more than 300 bytes of metadata.
It doesn't seem to be a typo, as the documentation states
The camera can produce metadata and the total size of such metadata
can't exceed the dwValue - as reported by GET_MAX request – times 1024
bytes less the size of a UsbVideoHeader metadata payload, for any
frame.
It looks like a design mistake though.
> Will send a patch with the updated documentation.
>
> > Some devices also don't support SET_CUR, in which case they should
> > report GET_MIN == GET_DEF == GET_MAX. I assume GET_CUR should then also
> > report the same value. Please also update the previous comment to
> > explain this, the GET_CUR value check above is more about handling
> > devices that always produce metadata than devices for which a driver has
> > enabled metadata production.
> >
> > This leads to another question: should we enable metadata generation
> > only when the metadata capture device is streaming ?
>
> This will lead to a lot of issues with very little benefit.
>
> We have no control over the order that the user will enable streamon
> in the metadata and "normal" video devices. And the device will not
> like that MSXU_CONTROL_METADATA changes during streamon.
>
> I have not seen any performance penalty by the 300 new bytes
> transferred when the metadata is on.
>
> > > > > + * us, the value from GET_MAX seems to work all the time.
> > > > > + */
> > > > > + ret = uvc_query_ctrl(dev, UVC_GET_MAX, entity->id, dev->intfnum,
> > > > > + MSXU_CONTROL_METADATA, data, sizeof(*data));
> > > > > + if (ret || !*data)
> > > > > + return 0;
> > > > > +
> > > > > + /*
> > > > > + * If we can set MSXU_CONTROL_METADATA, the device will report
> > > > > + * metadata.
> > > > > + */
> > > > > + ret = uvc_query_ctrl(dev, UVC_SET_CUR, entity->id, dev->intfnum,
> > > > > + MSXU_CONTROL_METADATA, data, sizeof(*data));
> > > > > + if (!ret)
> > > > > + dev->quirks |= UVC_QUIRK_MSXU_META;
> > > > > +
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > int uvc_meta_register(struct uvc_streaming *stream)
> > > > > {
> > > > > struct uvc_device *dev = stream->dev;
> > > > > @@ -185,9 +251,14 @@ int uvc_meta_register(struct uvc_streaming *stream)
> > > > > &uvc_meta_fops, &uvc_meta_ioctl_ops);
> > > > > }
> > > > >
> > > > > -void uvc_meta_init(struct uvc_device *dev)
> > > > > +int uvc_meta_init(struct uvc_device *dev)
> > > > > {
> > > > > unsigned int i = 0;
> > > > > + int ret;
> > > > > +
> > > > > + ret = uvc_meta_detect_msxu(dev);
> > > > > + if (ret)
> > > > > + return ret;
> > > > >
> > > > > dev->meta_formats[i++] = V4L2_META_FMT_UVC;
> > > > >
> > > > > @@ -201,4 +272,6 @@ void uvc_meta_init(struct uvc_device *dev)
> > > > >
> > > > > /* IMPORTANT: for new meta-formats update UVC_MAX_META_DATA_FORMATS. */
> > > > > dev->meta_formats[i++] = 0;
> > > > > +
> > > > > + return 0;
> > > > > }
> > > > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > > > > index 616adc417c62a58686beccbc440a5dfac0a2d588..a4c064c5e046f2a4adba742c8777a10619569606 100644
> > > > > --- a/drivers/media/usb/uvc/uvcvideo.h
> > > > > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > > > > @@ -757,7 +757,7 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
> > > > > void uvc_video_clock_update(struct uvc_streaming *stream,
> > > > > struct vb2_v4l2_buffer *vbuf,
> > > > > struct uvc_buffer *buf);
> > > > > -void uvc_meta_init(struct uvc_device *dev);
> > > > > +int uvc_meta_init(struct uvc_device *dev);
> > > > > int uvc_meta_register(struct uvc_streaming *stream);
> > > > >
> > > > > int uvc_register_video_device(struct uvc_device *dev,
> > > > > diff --git a/include/linux/usb/uvc.h b/include/linux/usb/uvc.h
> > > > > index bce95153e5a65613a710d7316fc17cf5462b5bce..ee19e9f915b8370c333c426dc1ee4202c7b75c5b 100644
> > > > > --- a/include/linux/usb/uvc.h
> > > > > +++ b/include/linux/usb/uvc.h
> > > > > @@ -29,6 +29,9 @@
> > > > > #define UVC_GUID_EXT_GPIO_CONTROLLER \
> > > > > {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, \
> > > > > 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x03}
> > > > > +#define UVC_GUID_MSXU_1_5 \
> > > > > + {0xdc, 0x95, 0x3f, 0x0f, 0x32, 0x26, 0x4e, 0x4c, \
> > > > > + 0x92, 0xc9, 0xa0, 0x47, 0x82, 0xf4, 0x3b, 0xc8}
> > > > >
> > > > > #define UVC_GUID_FORMAT_MJPEG \
> > > > > { 'M', 'J', 'P', 'G', 0x00, 0x00, 0x10, 0x00, \
> > > > >
--
Regards,
Laurent Pinchart
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