[Intel-gfx] [PATCH 10/10] drm/i915: Use MI_BATCH_BUFFER_START on 830/845

Chris Wilson chris at chris-wilson.co.uk
Mon Dec 14 08:58:54 PST 2015

On Mon, Dec 14, 2015 at 06:23:49PM +0200, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> MI_BATCH_BUFFER is nasty since it requires that userspace pass in the
> correct batch length.
> Let's switch to using MI_BATCH_BUFFER_START instead (like we do on
> other platforms). Then we don't have to specify the batch length
> at all, and the CS will instead execute until it sees the

Oh. My. Gosh. There's a BB_START?!!!

> We still need the batch length since we do the CS TLB workaround
> and copy the batch into the permanently pinned scratch object
> and execute it from there. But for this we can simply use the
> batch object length when the user hasn't specified the actual
> batch length. So specifying the batch length becomes just a
> way to optimize the batch copy a little bit.
> We lost batch_len from a bunch of igts (including the quiesce batch)
> so without this igt is utterly broken on 830/845. Also some igts such
> as gem_cpu_reloc never specified the batch_len and so didn't work.
> With MI_BATCH_BUFFER_START we don't have to fix up igt every time
> someone forgets that 830/845 exist.
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Looks sane.

Chris Wilson, Intel Open Source Technology Centre

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