[Intel-gfx] [PATCH] drm/i915: Don't try to use DDR DVFS on CHV when disabled in the BIOS

[Ville Syrjälä]

On Tue, Sep 08, 2015 at 09:16:11PM +0100, Chris Wilson wrote:
> On Tue, Sep 08, 2015 at 09:05:12PM +0300, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > If one disables DDR DVFS in the BIOS, Punit will apparently ignores
> > all DDR DVFS request. Currently we assume that DDR DVFS is always
> > operational, which leads to errors in dmesg when the DDR DVFS requests
> > time out.
> > 
> > Fix the problem by gently prodding Punit during driver load to find out
> > whether it will respond to DDR DVFS requests. If the request times out,
> > we assume that DDR DVFS has been permanenly disabled in the BIOS and
> > no longer perster the Punit about it.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91629
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Code looks clean (just a minor duplicated vlv_read(DDR_SETUP2) in
> setup).

Yeah I suppose I could have reused the orignal value read, or reassign
val also in wait_for().

> Would it make sense to disable dvfs after a failure as well,
> then the user is shown a single DRM_ERROR at runtime and we should
> recover (by not going to the full WM next time)?

I wouldn't expect any failures after we've determined that it works.
That would indicate Punit going belly up or something, and then I'm
not sure anything would work anymore.

So I would hold on doing that unless someone actually hits such a
problem.

-- 
Ville Syrjälä
Intel OTC