This patch series was sent to libcamera-devel instead of linux-media. I've now fixed that mistake, sorry the noise. Please reply to the series sent to the right mailing list. On Thu, Aug 22, 2024 at 06:35:20PM +0300, Laurent Pinchart wrote: > Hello, > > This patch series improves the link validation helpers to make it easier > for drivers to validate all links in a pipeline. > > The vast majority of drivers use the v4l2_subdev_link_validate() > function as their .link_validate() handler for subdevs. This correctly > validates subdev-to-subdev links. For links between subdevs and video > capture devices, a few drivers implement the .link_validate() operation > of their video devices, while others implement manual validation in > their .streamon() handler, or don't implement validation at all. Links > between video output devices are in an even worse state, as the link > validation logic at pipeline start time does not call the > .link_validate() operation on the source side of a link, leaving manual > validation in .streamon() the only option. Adding insult to injury, > v4l2_subdev_link_validate() prints a warning when the link's source is > not a subdev, which forces drivers to implement a manual subdev link > validation handler for subdevs connected to output video nodes. > > It turns out that v4l2_subdev_link_validate() is even used in the > .link_validate() implementation of video devices by two drivers. This is > clearly wrong, and is addressed by patches 1/7 to 3/7. Note that patch > 3/7 should ideally implement real validation of the link between the > subdev and video capture device, but that requires understanding of the > driver's logic as well as testing, so I have left it out as an exercise > for the driver's maintainer. The patch doesn't introduce any regression. > > Patch 4/7 then starts refactoring the v4l2_subdev_link_validate() to > separate the current warning in two categories, with a WARN_ON() for an > issue that indicates a clear driver bug (and does not occur in any > driver in mainline at the moment), and keeping the pr_warn_once() for > other issues that are present in multiple drivers. > > Patch 5/7 continues with expanding v4l2_subdev_link_validate() to better > support links from video output devices to subdevs, delegating the > validation to the video output device's .link_validate() operation. This > allows using v4l2_subdev_link_validate() for all subdevs in a driver, > regardless of whether they are connected to other subdevs, video capture > devices or video output devices, and implementing all the link > validation for video devices in their .link_validate() operation. > > Patches 6/7 and 7/7 then address the v4l2_subdev_link_validate() warning > for the vsp1 driver. Patch 6/7 silences the warning. This is > unfortunately done with a workaround, as the ideal implementation, > moving all validation for video devices to their .link_validate() > operation as showcased in patch 7/7, breaks operation of the vsp1 unit > test suite. While that is fixable in the test suite, it indicates that > other userspace applications may also break as a result. > > To my great sadness, I had to mark patch 7/7 as [DNI]. This does not > make the v4l2_subdev_link_validate() improvements in patch 5/7 > pointless, as they are useful for new drivers, as well as drivers that > don't include multiple video devices in a pipeline. > > Laurent Pinchart (7): > media: microchip-isc: Drop v4l2_subdev_link_validate() for video > devices > media: sun4i_csi: Implement link validate for sun4i_csi subdev > media: sun4i_csi: Don't use v4l2_subdev_link_validate() for video > device > media: v4l2-subdev: Refactor warnings in v4l2_subdev_link_validate() > media: v4l2-subdev: Support hybrid links in > v4l2_subdev_link_validate() > media: renesas: vsp1: Implement .link_validate() for video devices > [DNI] media: renesas: vsp1: Validate all links through > .link_validate() > > .../platform/microchip/microchip-isc-base.c | 19 +--- > .../media/platform/renesas/vsp1/vsp1_video.c | 104 +++++++++--------- > .../platform/sunxi/sun4i-csi/sun4i_csi.c | 12 ++ > drivers/media/v4l2-core/v4l2-subdev.c | 50 +++++++-- > include/media/v4l2-subdev.h | 6 + > 5 files changed, 115 insertions(+), 76 deletions(-) > > > base-commit: a043ea54bbb975ca9239c69fd17f430488d33522 -- Regards, Laurent Pinchart
