[Intel-gfx] [PATCH] drm/i915/guc: Don't read SOFT_SCRATCH(15) on MMIO error

[Chris Wilson]

Quoting Michal Wajdeczko (2018-05-29 16:10:44)
> On Tue, 29 May 2018 16:54:12 +0200, Chris Wilson  
> <chris at chris-wilson.co.uk> wrote:
> 
> > Quoting Michal Wajdeczko (2018-05-28 18:16:18)
> >> SOFT_SCRATCH(15) is used by GuC for sending MMIO GuC events to host and
> >> those events are now handled by intel_guc_to_host_event_handler_mmio().
> >>
> >> We should not try to read it on MMIO action error as 1) we may be using
> >> different set of registers for GuC MMIO communication, and 2) GuC may
> >> use CTB mechanism for sending events to host.
> >
> > Ok.
> >
> >> While here, upgrade error message to DRM_ERROR.
> >
> > Does the error help? What do you want to convey to the user? For error
> > handling, we want to propagate the result back anyway for the caller has
> > to decide what to do next.
> 
> We are propagating error code to the caller, but since any error from the
> GuC is unexpected, we should rather always log it and don't rely on the
> caller or drm debug for that. Note that in case of CTB we also log received
> errors using DRM_ERROR (see intel_guc_send_ct).

But whose error? Ours or the hw? We expect hw errors, or should ;)

But mostly from the pov of the message, is this the right information to
flag as the error or does the caller have better context?
-Chris