[PATCH 5/9] drm/i915: Enable i915 perf stream for Haswell OA unit

[Robert Bragg]

On Wed, Apr 20, 2016 at 11:46 PM, Chris Wilson <chris at chris-wilson.co.uk>
wrote:

> On Wed, Apr 20, 2016 at 03:23:10PM +0100, Robert Bragg wrote:
> > +static void gen7_init_oa_buffer(struct drm_i915_private *dev_priv)
> > +{
> > +     /* Pre-DevBDW: OABUFFER must be set with counters off,
> > +      * before OASTATUS1, but after OASTATUS2
> > +      */
> > +     I915_WRITE(GEN7_OASTATUS2, dev_priv->perf.oa.oa_buffer.gtt_offset |
> > +                OA_MEM_SELECT_GGTT); /* head */
> > +     I915_WRITE(GEN7_OABUFFER, dev_priv->perf.oa.oa_buffer.gtt_offset);
> > +     I915_WRITE(GEN7_OASTATUS1, dev_priv->perf.oa.oa_buffer.gtt_offset |
> > +                OABUFFER_SIZE_16M); /* tail */
> > +
> > +     /* On Haswell we have to track which OASTATUS1 flags we've
> > +      * already seen since they can't be cleared while periodic
> > +      * sampling is enabled.
> > +      */
> > +     dev_priv->perf.oa.gen7_latched_oastatus1 = 0;
> > +
> > +     /* We have a sanity check in gen7_append_oa_reports() that
> > +      * looks at the report-id field to make sure it's non-zero
> > +      * which relies on the assumption that new reports are
> > +      * being written to zeroed memory...
> > +      */
> > +     memset(dev_priv->perf.oa.oa_buffer.addr, 0, SZ_16M);
>
> You allocated zeroed memory.
>

yup. currently I have this memset here because we may re-init the buffer if
the stream is disabled then re-enabled (via I915_PERF_IOCTL_ENABLE) or if
we have to reset the unit on error. In these cases there may be some number
of reports in the buffer with non-zero report-id fields while we still want
to be sure new reports are being written to zereod memory so that the
sanity check that report-id != 0 will continue to be valid.

I've had it in mind to consider optimizing this at some point to minimize
how much of the buffer is cleared, maybe just for the _DISABLE/_ENABLE case
where I'd expect the buffer will mostly be empty before disabling the
stream.

- Robert


-Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre
>
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