[Intel-gfx] [PATCH] drm/i915: detect wrong MCH watermark values

[Ben Widawsky]

On Sat, Feb 09, 2013 at 09:03:42PM +0100, Daniel Vetter wrote:
> Some early bios versions seem to ship with the wrong tuning values for
> the MCH, possible resulting in pipe underruns under load. Especially
> on DP outputs this can lead to black screen, since DP really doesn't
> like an occasional whack from an underrun.
> 
> Unfortunately the registers seem to be locked after boot, so the only
> thing we can do is politely point out issues and suggest a BIOS
> upgrade.
> 
> Arthur Runyan pointed us at this issue while discussion DP bugs - thus
> far no confirmation from a bug report yet that it helps. But at least
> some of my machines here have wrong values, so this might be useful in
> understanding bug reports.
> 
> v2: After a bit more discussion with Art and Ben we've decided to only
> the check the watermark values, since the OREF ones could be be a
> notch more aggressive on certain machines.
> 
> Cc: Ben Widawsky <ben at bwidawsk.net>
> Cc: Runyan, Arthur J <arthur.j.runyan at intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

I wouldn't mind if you printed the OREF values, even if you didn't use
them to detect.

But,
Reviewed-by: Ben Widawsky <ben at bwidawsk.net>

[snip]

-- 
Ben Widawsky, Intel Open Source Technology Center