Re: [PATCH 1/2] drm/i915: Remove the MI_FLUSH_ENABLE setting.

[Kenneth Graunke <kenneth@whitecape.org>]

On 01/19/2012 10:50 AM, Eric Anholt wrote:
> We have always been using the wrong bit -- it's bit 12.  However, the
> bit also doesn't do anything -- hardware has always accepted the
> MI_FLUSH command even when it was specced not to.
>
> Given that there is only one MI_FLUSH emitted in all of the driver
> stack on gen6+ (in i965_video.c of the 2d driver, and it should be
> using other code to do its flush instead), just remove the MI_FLUSH
> enable instead of trying to fix it.
>
> Signed-off-by: Eric Anholt<eric@anholt.net>
> ---
>   drivers/gpu/drm/i915/intel_ringbuffer.c |    2 --
>   1 files changed, 0 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 2df35e3..d21346b 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -389,8 +389,6 @@ static int init_render_ring(struct intel_ring_buffer *ring)
>
>   	if (INTEL_INFO(dev)->gen>  3) {
>   		int mode = VS_TIMER_DISPATCH<<  16 | VS_TIMER_DISPATCH;
> -		if (IS_GEN6(dev) || IS_GEN7(dev))
> -			mode |= MI_FLUSH_ENABLE<<  16 | MI_FLUSH_ENABLE;
>   		I915_WRITE(MI_MODE, mode);
>   		if (IS_GEN7(dev))
>   			I915_WRITE(GFX_MODE_GEN7,

Everything using MI_FLUSH on SNB+ ought to be converted to PIPE_CONTROL. 
  It sounds like everything except i965_video is there already.  There's 
still the issue of old userspace, but...given that we were setting the 
wrong bit and _not_ setting the actual MI_FLUSH enable bit...it seems 
like this patch shouldn't break things.

I'm all in favor of removing this code, as it's definitely a lie.

For both patches:
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>