On 05/27/2014 12:17 AM, Laurent Pinchart wrote: > Hello, > > This RFC patch series attempts to clean up the current ARGB format mess. > > The core issue is that the existing ARGB formats are ill-defined. The V4L2 > specification doesn't clearly document how the alpha bits should behave. > Drivers have thus used the same formats in different, incompatible ways, and > applications now rely on the driver-specific behaviours. In a word, that's a > mess. > > I've discussed the issue in the #v4l channel a couple of days ago and we came > up to the conclusion that the best (or least painful) way to fix the problem > is to define new clean XRGB and ARGB formats, and consider the existing > formats as deprecated (meaning that no new driver should use them, they won't > disappear in a couple of months, as that would break userspace). > > The first patch adds the new XRGB and ARGB formats and documents them. Question: should we add all XRGB and ARGB formats even if drivers do not use them? Or just those that are actually used? > It > purposely includes no core code to handle backward compatibility for existing > drivers that may wish to move to the new formats. The reason is that I would > first like to get feedback on the proposal before working on compat code, and > I believe we should first implement the compat code in a couple of drivers and > then see how the approach could be generalized, if possible at all. > > The second patch allows using the ALPHA_COMPONENT control on output devices to > support an ARGB use case documented in the first patch. One possible > shortcoming of reusing the existing control is that a mem-to-mem driver that > exposes an output and a capture queue on a single video node through the same > file handle wouldn't be able to set different alpha component values on the > two queues. I'm not sure whether that use case is real though, it seems weird > to me to set a fixed alpha value on one side to request a different fixed > alpha value on the other side. I prefer a CAP_ALPHA_COMPONENT control. It's easy to add a capture-specific control now, it's much harder to change it in the future. Regards, Hans > > Laurent Pinchart (2): > v4l: Add ARGB and XRGB pixel formats > DocBook: media: Document ALPHA_COMPONENT control usage on output > devices > > Documentation/DocBook/media/v4l/controls.xml | 17 +- > .../DocBook/media/v4l/pixfmt-packed-rgb.xml | 415 ++++++++++++++++++++- > include/uapi/linux/videodev2.h | 8 + > 3 files changed, 413 insertions(+), 27 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
