On 07/31/2011 08:32 PM, Geert Uytterhoeven wrote: > On Thu, Jul 28, 2011 at 12:51, Laurent Pinchart > <laurent.pinchart at ideasonboard.com> wrote: >>> As for struct fb_var_screeninfo fields to support switching to a FOURCC >>> mode, I also prefer an explicit dedicated flag to specify switching to it. >>> Even though using FOURCC doesn't fit under the notion of a videomode, using >>> one of .vmode bits is too tempting, so, I would actually take the plunge and >>> use FB_VMODE_FOURCC. >> >> Another option would be to consider any grayscale> 1 value as a FOURCC. I've >> briefly checked the in-tree drivers: they only assign grayscale with 0 or 1, >> and check whether grayscale is 0 or different than 0. If a userspace >> application only sets grayscale> 1 when talking to a driver that supports >> the >> FOURCC-based API, we could get rid of the flag. >> >> What can't be easily found out is whether existing applications set grayscale >> to a> 1 value. They would break when used with FOURCC-aware drivers if we >> consider any grayscale> 1 value as a FOURCC. Is that a risk we can take ? > > I think we can. I'd expect applications to use either 1 or -1 (i.e. > all ones), both are > invalid FOURCC values. > > Still, I prefer the nonstd way. > And limiting traditional nonstd values to the lowest 24 bits (there > are no in-tree > drivers using the highest 8 bits, right?).
Okay, it would be okay for me to - write raw FOURCC values in nonstd, enable FOURCC mode if upper byte != 0 - not having an explicit flag to enable FOURCC - in FOURCC mode drivers must set visual to FB_VISUAL_FOURCC - making support of FOURCC visible to userspace by capabilites |= FB_CAP_FOURCC The capabilities is not strictly necessary but I think it's very useful as - it allows applications to make sure the extension is supported (for example to adjust the UI) - it allows applications to distinguish whether a particular format is not supported or FOURCC at all - it allows signaling further extensions of the API - it does not hurt, one line per driver and still some bytes in fixinfo free So using it would look like this: - the driver must have capabilities |= FB_CAP_FOURCC - the application may check capabilities to know whether FOURCC is supported - the application may write a raw FOURCC value in nonstd to request changing to FOURCC mode with this format - when the driver switches to a FOURCC mode it must have visual = FB_VISUAL_FOURCC and the current FOURCC format in nonstd - the application should check visual and nonstd to make sure it gets what it wanted So if there are no strong objections against this I think we should implement it. I do not really care whether we use a union or not but I think if we decide to have one it should cover all fields that are undefined/unused in FOURCC mode. Hope we can find anything that everyone considers acceptable, Florian Tobias Schandinat
