[Intel-gfx] [PATCH 1/3] drm/i915: Check if the stolen memory "reserved" area is enabled or not

[Chris Wilson]

Quoting Paulo Zanoni (2017-11-14 20:12:41)
> Em Qui, 2017-11-02 às 17:17 +0200, Ville Syrjala escreveu:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Apparently there are some machines that put semi-sensible looking
> > values
> > into the stolen "reserved" base and size, except those values are
> > actually
> > outside the stolen memory. There is a bit in the register which
> > supposedly could tell us whether the reserved area is even enabled or
> > not. Let's check for that before we go trusting the base and size.
> 
> If this is such a problem since g4x, why didn't we spot it earlier? It
> would be nice if you could explain in the commit message (or at least
> in this email) what are the consequences you're seeing that made you
> realize about this problem. Did something actually explode? I'm
> genuinely curious.

The consequence is that we disable stolen; the machine keeps on working
quite happily. Only fbc actually depends on stolen allocation to
function, and no one complains if fbc is disabled. (There's a sketch out
there that we could use a contiguous allocation for fbc if we run out of
stolen.) Internal hw functions are oblivious to our qualms about the
location of stolen and whether some other device is using the same
physical address for its trampoline.
-Chris