[Intel-gfx] [PATCH 2/2] drm/i915: Default to mmio flips on VLV

[Chris Wilson]

On Wed, May 28, 2014 at 12:42:02PM +0530, sourab.gupta at intel.com wrote:
> From: Sourab Gupta <sourab.gupta at intel.com>
> 
> This patch is for using mmio flips by default on VLV.
> The module parameter controlling use of MMIO flips allows us to
> control the default behaviour, which is set true for VLV and false
> elsewhere.
> 
> Signed-off-by: Sourab Gupta <sourab.gupta at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_params.c   |  5 +++--
>  drivers/gpu/drm/i915/intel_display.c | 12 ++++++++++++
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index e0d44df..a99accc 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -48,7 +48,7 @@ struct i915_params i915 __read_mostly = {
>  	.disable_display = 0,
>  	.enable_cmd_parser = 1,
>  	.disable_vtd_wa = 0,
> -	.use_mmio_flip = 0,
> +	.use_mmio_flip = -1,
>  };
>  
>  module_param_named(modeset, i915.modeset, int, 0400);
> @@ -159,4 +159,5 @@ MODULE_PARM_DESC(enable_cmd_parser,
>  		 "Enable command parsing (1=enabled [default], 0=disabled)");
>  
>  module_param_named(use_mmio_flip, i915.use_mmio_flip, bool, 0600);
> -MODULE_PARM_DESC(use_mmio_flip, "use MMIO flips (default: false)");
> +MODULE_PARM_DESC(use_mmio_flip, "use MMIO page flips "
> +		"(default: -1 (use per-chip default))");
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index f11abfb..312a9a1 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -9197,6 +9197,18 @@ static bool intel_use_mmio_flip(struct drm_device *dev)
>  	if (i915.use_mmio_flip == 0)
>  		return false;
>  
> +	/* On Valleyview, use MMIO flips by default, for Media Power Well
> +	 * residency optimization. The other alternative of having Render
> +	 * ring based flip calls is not being used, as the performance(FPS)
> +	 * of certain 3D Apps gets severly affected.
> +	 */

Pray tell, what RCS flips?

This seems to only tell one half of the story and would seem to imply
that only using mmio for the BSD ring would be preferrable. The current
override doesn't look useful enough to do an independent study of BCS vs
mmio flips for all workloads.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre