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

[Ville Syrjälä]

On Mon, Jun 08, 2015 at 12:12:41PM +0300, Mika Kuoppala wrote:
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > 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?
> >
> 
> Yes that is the sole purpose. I don't see any drawback.

C likes to promote most things to int anyway, so I'm not sure what this
widening is all about.

-- 
Ville Syrjälä
Intel OTC