Re: [PATCH] drm/i915: Shift driver's HWSP usage out of reserved range

From: Daniel Vetter <daniel@ffwll.ch>
To: Dave Gordon <david.s.gordon@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Shift driver's HWSP usage out of reserved range
Date: Tue, 24 Feb 2015 00:27:52 +0100	[thread overview]
Message-ID: <20150223232752.GV24485@phenom.ffwll.local> (raw)
In-Reply-To: <54E5FA28.8020407@intel.com>

On Thu, Feb 19, 2015 at 02:58:48PM +0000, Dave Gordon wrote:
> On 18/02/15 11:48, Thomas Daniel wrote:
> > As of Gen6, the general purpose area of the hardware status page has shrunk and
> > now begins at dword 0x30.  i915 driver uses dword 0x20 to store the seqno which
> > is now reserved.  So shift our HWSP dwords up into the general purpose range
> > before this bites us.

It would be really interesting to know what exactly the hw does with
offsets below 0x30 ... it might explain some of the bugs we've seen. Can
you please digg that out so that I can amend the commit message?

> > Signed-off-by: Thomas Daniel <thomas.daniel@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_ringbuffer.h |    7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> > index b6c484f..39183fc 100644
> > --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> > @@ -373,11 +373,12 @@ intel_write_status_page(struct intel_engine_cs *ring,
> >   * 0x06: ring 2 head pointer (915-class)
> >   * 0x10-0x1b: Context status DWords (GM45)
> >   * 0x1f: Last written status offset. (GM45)
> > + * 0x20-0x2f: Reserved (Gen6+)
> >   *
> > - * The area from dword 0x20 to 0x3ff is available for driver usage.
> > + * The area from dword 0x30 to 0x3ff is available for driver usage.
> >   */
> > -#define I915_GEM_HWS_INDEX		0x20
> > -#define I915_GEM_HWS_SCRATCH_INDEX	0x30
> > +#define I915_GEM_HWS_INDEX		0x30
> > +#define I915_GEM_HWS_SCRATCH_INDEX	0x40
> >  #define I915_GEM_HWS_SCRATCH_ADDR (I915_GEM_HWS_SCRATCH_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
> >  
> >  void intel_unpin_ringbuffer_obj(struct intel_ringbuffer *ringbuf);
> 
> Well, nothing much can go wnorg here!
> 
> Reviewed-by: Dave Gordon <david.s.gordon@intel.com>

Anyway for now queued for -next, thanks for the patch.
-Daniel

> 
> But just FYI, these will all get changed again when we add support for
> preemption (: because then we'll need more than one place to store
> 'sequence numbers' :)
> 
> .Dave.
> 
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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