Re: OMAP:DSS: possible bug in WAITFOR_VSYNC ioctl

[Paul Mundt <lethal@linux-sh.org>]

On Tue, Nov 30, 2010 at 03:34:40PM +0900, Paul Mundt wrote:
> On Fri, Nov 26, 2010 at 02:55:39PM +0200, Ville Syrj?l? wrote:
> > On Fri, Nov 26, 2010 at 05:38:11PM +0530, ext Hiremath, Vaibhav wrote:
> > > With this finding, in case of OMAP3 we have to use OMAPFB_WAITFORGO
> > > (breaking standard applications).
> > 
> > Applications using the standard fbdev API won't work with manual update
> > displays anyway. You need omapfb specific code to handle it so having
> > another small difference is not a big deal.
> > 
> > In DirectFB the that's trivial since there's already a simple omap
> > gfxdriver where you could override the default flip functionality with
> > WAITFORGO based stuff.
> > 
> > Or, as I said, you could add another standard ioctl and fix up userspace
> > to use it where appropriate and if the kernel driver supports it.
> > 
> It seems like the WAITFORGO semantics could be layered on top of drivers
> using deferred I/O pretty easily, but the question is whether this is
> something that userspace plans to make general use of or not. If the only
> user of it in userspace code is OMAP-specific, then there's probably not
> a lot of point in moving it over to be generic, but if there are
> sufficient cases where userspace cares about this information independent
> of WAITFORVSYNC for manual update displays, then we can certainly look at
> moving it over for those cases.

Also, WAITFORGO is a pretty abysmal name. It seems like what you want is
a WAITFORHWSYNC or something similar.