[Intel-gfx] [PATCH 2/2] drm/i915: Let hardware keep track of ctx buf read pointer

[Daniel, Thomas]

> -----Original Message-----
> From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org] On Behalf Of
> Chris Wilson
> Sent: Saturday, May 23, 2015 5:11 PM
> To: Mika Kuoppala
> Cc: intel-gfx at lists.freedesktop.org; miku at iki.fi
> Subject: Re: [Intel-gfx] [PATCH 2/2] drm/i915: Let hardware keep track of ctx
> buf read pointer
> 
> On Fri, May 22, 2015 at 08:17:22PM +0300, Mika Kuoppala wrote:
> > We initialize the internal read pointer to zero on init/reset,
> > but only the reset will actually zero the write pointer.
> > This means that on module reload we might re-read context
> > status buffers that were written prior reload.
> >
> > It is safest just to let the hardware keep track of the read pointer,
> > so that we get valid value as there is no driver state involved.
> >
> > Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_debugfs.c     |  6 +++---
> >  drivers/gpu/drm/i915/intel_lrc.c        | 11 ++++-------
> >  drivers/gpu/drm/i915/intel_ringbuffer.h |  2 +-
> >  3 files changed, 8 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
> b/drivers/gpu/drm/i915/i915_debugfs.c
> > index fece922..b079dd3 100644
> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > @@ -2026,8 +2026,8 @@ static int i915_execlists(struct seq_file *m, void
> *data)
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> >  	struct intel_engine_cs *ring;
> >  	u32 status_pointer;
> > -	u8 read_pointer;
> > -	u8 write_pointer;
> > +	u32 read_pointer;
> > +	u32 write_pointer;
> 
> I don't follow this change. It seems like this is to avoid having to
> explicitly widen the type when converting the 32bit register value later
> on?
> 
> Otherwise I agree very much with the sentiment of the patch!
> -Chris
Do we still need to keep the sw pointer as a WA for this register field not being restored during power context restore on certain BDW GT3?
 
Thomas.