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

[Chris Wilson]

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). 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)?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre