-----Original Message-----
From: Ville Syrjälä [mailto:ville.syrjala@nokia.com]
Sent: Friday, November 26, 2010 6:26 PM
To: Hiremath, Vaibhav
Cc: Måns Rullgård; linux-omap@vger.kernel.org; linux-fbdev@vger.kernel.org
Subject: Re: OMAP:DSS: possible bug in WAITFOR_VSYNC ioctl

On Fri, Nov 26, 2010 at 05:38:11PM +0530, ext Hiremath, Vaibhav wrote:

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-----Original Message-----
From: Hiremath, Vaibhav
Sent: Friday, November 26, 2010 5:34 PM
To: 'Måns Rullgård'; linux-omap@vger.kernel.org
Subject: RE: OMAP:DSS: possible bug in WAITFOR_VSYNC ioctl

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-----Original Message-----
From: linux-omap-owner@vger.kernel.org [mailto:linux-omap-
owner@vger.kernel.org] On Behalf Of Måns Rullgård
Sent: Friday, November 26, 2010 2:09 PM
To: linux-omap@vger.kernel.org
Subject: Re: OMAP:DSS: possible bug in WAITFOR_VSYNC ioctl

"Hiremath, Vaibhav" [off-list ref] writes:

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-----Original Message-----
From: Ville Syrjälä [mailto:ville.syrjala@nokia.com]
Sent: Wednesday, November 24, 2010 10:01 PM
To: Hiremath, Vaibhav
Cc: Tomi Valkeinen; linux-omap@vger.kernel.org
Subject: Re: OMAP:DSS: possible bug in WAITFOR_VSYNC ioctl

On Wed, Nov 24, 2010 at 03:39:44PM +0530, ext Hiremath, Vaibhav

wrote:

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-----Original Message-----
From: Tomi Valkeinen [mailto:tomi.valkeinen@nokia.com]
Sent: Wednesday, November 24, 2010 2:28 PM
To: Hiremath, Vaibhav
Cc: linux-omap@vger.kernel.org
Subject: Re: OMAP:DSS: possible bug in WAITFOR_VSYNC ioctl

On Tue, 2010-11-23 at 23:46 +0530, ext Hiremath, Vaibhav

wrote:

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Hi,

<snip>

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<snip..>

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As far as WAITFORGO is concerned, I think GO bit concept is
something OMAP notion/term and doesn't make sense to standardize
it. Atleast I am not aware of any other architecture having GO bit.

Naming is minor detail.  Feel free to suggest a better one.

[Hiremath, Vaibhav] If I fail to convince on this, then I think the

only

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left option is to make WAITFORGO ioctl generic. And put a disclaimer

on

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WAITFORVSYNC, it must not be used in panning use-case.

[Hiremath, Vaibhav] Also let me bring another point here,

If I understand correctly most of the application libraries (DirectFB, X,

etc..) does use FBIO_WAITFORVSYNC to synchronize with HW, and manage ping
pong mechanism.

DirectFB uses it also for waiting for vsync.

[Hiremath, Vaibhav] Mat,

I am not expert on DirectFb stuff; can you please help me to understand what the use-case is? What DirectFB does/expects on this?

Thanks,
Vaibhav

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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.

--
Ville Syrjälä