[PATCH] drm: Don't pass negative delta to ktime_sub_ns()

[Chris Wilson]

On Wed, Jun 12, 2013 at 11:58:44AM +0200, Michel Dänzer wrote:
> From: Michel Dänzer <michel.daenzer at amd.com>
> 
> It takes an unsigned value. This happens not to blow up on 64-bit
> architectures, but it does on 32-bit, causing
> drm_calc_vbltimestamp_from_scanoutpos() to calculate totally bogus
> timestamps for vblank events. Which in turn causes e.g. gnome-shell to
> hang after a DPMS off cycle with current xf86-video-ati Git.
> 
> Cc: stable at vger.kernel.org
> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>

iiuc, this occurs when compensating for the early vblank interrupt.
However,

#define ktime_sub_ns(kt, nsval) \
    ({ (ktime_t){ .tv64 = (kt).tv64 - (nsval) }; })

so both tv64 and delta_ns are s64. I am not seeing the unsigned
promotion bug here.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre