[Intel-gfx] [PATCH v1 2/4] drm/i915: Add provision to extend Golden context batch

[Chris Wilson]

On Fri, Jul 17, 2015 at 07:37:45PM +0300, Mika Kuoppala wrote:
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > On Fri, Jul 17, 2015 at 05:08:52PM +0100, Arun Siluvery wrote:
> >> The Golden batch carries 3D state at the beginning so that HW starts with
> >> a known state. It is carried as a binary blob which is auto-generated from
> >> source. The idea was it would be easier to maintain and keep the complexity
> >> out of the kernel which makes sense as we don't really touch it. However if
> >> you really need to update it then you need to update generator source and
> >> keep the binary blob in sync with it.
> >> 
> >> There is a need to patch this in bxt to send one additional command to enable
> >> a feature. A solution was to patch the binary data with some additional
> >> data structures (included as part of auto-generator source) but it was
> >> unnecessarily complicated.
> >> 
> >> Chris suggested the idea of having a secondary batch and execute two batch
> >> buffers. It has clear advantages as we needn't touch the base golden batch,
> >> can customize secondary/auxiliary batch depending on Gen and can be carried
> >> in the driver with no dependencies.
> >> 
> >> This patch adds support for this auxiliary batch which is inserted at the
> >> end of golden batch and is completely independent from it. Thanks to Mika
> >> for the preliminary review.
> >> 
> >> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >> Cc: Armin Reese <armin.c.reese at intel.com>
> >> Signed-off-by: Arun Siluvery <arun.siluvery at linux.intel.com>
> >> ---
> >>  drivers/gpu/drm/i915/i915_gem_render_state.c | 27 +++++++++++++++++++++++++++
> >>  drivers/gpu/drm/i915/i915_gem_render_state.h |  2 ++
> >>  drivers/gpu/drm/i915/intel_lrc.c             |  6 ++++++
> >>  3 files changed, 35 insertions(+)
> >> 
> >> diff --git a/drivers/gpu/drm/i915/i915_gem_render_state.c b/drivers/gpu/drm/i915/i915_gem_render_state.c
> >> index b6492fe..b86e382 100644
> >> --- a/drivers/gpu/drm/i915/i915_gem_render_state.c
> >> +++ b/drivers/gpu/drm/i915/i915_gem_render_state.c
> >> @@ -73,6 +73,15 @@ free_gem:
> >>  	return ret;
> >>  }
> >>  
> >> +#define OUT_BATCH(batch, i, val)				\
> >> +	do {							\
> >> +		if (WARN_ON((i) >= PAGE_SIZE / sizeof(u32))) {	\
> >
> > We have to be slightly more careful here, as we don't have the full page
> > available since we put render state into the high arena of the golden
> > bb. Something like WARN_ON(i > PAGE/sizeof(u32) || (batch)[i]) should
> > suffice.
> >
> 
> Null state gen makes the final batch with two passes. First
> it builds command and state separately. And when size of both
> are know, it compacts by relocating the state right after
> the commands (+some alignment).
> 
> So we should have the rest of the page usable for auxillary
> commands here as we have already copied the state part
> also.

Ta. Maybe add some words of enlightenment here for future me as well?
Also we will need to document that the kernel then relies on the packing
to add extra commands after the batch to the null state generator.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre