[Intel-gfx] [PATCH 05/15] drm/i915/gt: Ignore forcewake acquisition for posting_reads

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-07-03 12:26:36)
> 
> On 03/07/2019 10:17, Chris Wilson wrote:
> > We don't care about the result of the read, so it may be garbage, we
> > only care that the mmio is flushed. As such, we can forgo using an
> > individual forcewake and lock around any posting-read for an engine.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_engine.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
> > index 557b08b13feb..0331e9ac2485 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> > @@ -51,7 +51,7 @@ struct drm_printer;
> >   #define ENGINE_READ16(...)  __ENGINE_READ_OP(read16, __VA_ARGS__)
> >   #define ENGINE_READ(...)    __ENGINE_READ_OP(read, __VA_ARGS__)
> >   #define ENGINE_READ_FW(...) __ENGINE_READ_OP(read_fw, __VA_ARGS__)
> > -#define ENGINE_POSTING_READ(...) __ENGINE_READ_OP(posting_read, __VA_ARGS__)
> > +#define ENGINE_POSTING_READ(...) __ENGINE_READ_OP(posting_read_fw, __VA_ARGS__)
> >   #define ENGINE_POSTING_READ16(...) __ENGINE_READ_OP(posting_read16, __VA_ARGS__)
> >   
> >   #define ENGINE_READ64(engine__, lower_reg__, upper_reg__) \
> > 
> 
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Can we apply this to all posting reads? (intel_uncore_posting_read*)

I briefly considered it, but was too lazy to think beyond the current
set. What gave me pause for concern was intel_gt_flush_ggtt_writes()
where we have to worry about overlapping mmio access causing gen7 to
explode, generalising the lock drop is tricky.
-Chris