[Intel-gfx] [PATCH 1/2] drm/i915/lrc: Clear context restore/save inhibit flags for new contexts

[Chris Wilson]

Quoting Michel Thierry (2018-01-25 17:49:49)
> On 1/25/2018 3:24 AM, Chris Wilson wrote:
> > CTX_CONTEXT_CONTROL (CTX_SR_CTL) operates as a masked register and so
> > will only apply the bits that are selected by the upper half. In the
> > case of selectively enabling sr inhibit, this may mean the context keeps
> > the current setting (so forgetting to save the context later, eventually
> > leading to a very upset GPU!).
> 
> Oops, true no one would clear Context Save Inhibit once it's set.
> 
> > 
> > Fixes: d2b4b97933f5 ("drm/i915: Record the default hw state after reset upon load")
> Does it really fixes this one ^^^?

It's a stretch, I don't have an observed bug, but I felt it was sensible
for completeness.
 
> Restore Inhibit has this note: "This is not a true register bit.... This 
> bit will always be in clear state on a context save of this bit". Maybe 
> that's why didn't see any problems. But it doesn't hurt being paranoid.

Paranoid is my middle name. Well it would be if the HW wasn't out to get
me.
-Chris