[Intel-gfx] [PATCH] [RFC] drm/i915: Unmask all render responses for SNB

[Ben Widawsky]

On Fri, 23 Sep 2011 11:21:29 +0100
Chris Wilson <chris at chris-wilson.co.uk> wrote:

> On SandyBridge in order to receive an event on the RENDER ring, you
> first must unmask the corresponding bit in the DERRMR (Display Engine
> Render Response Mask Register). This register is not accessible from a
> non-secure MI_LOAD_REGISTER_IMM so resort to unmasking all events upon
> initialisation. Presumably this leads to an undesirable increase in
> PCI traffic (possibly 4 additional wakeups per vblank per active
> pipe).
> 
> More tricky solutions include extending EXECBUFFER to include a
> request to enable the appropriate render response and for the kernel
> to unmask and reset around the batch. Also we need to include a flag
> to indicate that it is safe to use MI_WAIT_FOR_EVENT as well.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---

Sounds good, but...

{WA} Do not cause more than one display event to be reported in the render
response.  Either mask off all but one event, unmasking one bit in this
register, or never initiate more than one event.