[PATCH v4 05/16] drm/i915: Disable the "binder"

[Paz Zcharya]

On Thu, Jan 25, 2024 at 12:27:36PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Now that the GGTT PTE updates go straight to GSMBASE (bypassing
> GTTMMADR) there should be no more risk of system hangs? So the
> "binder" (ie. update the PTEs via MI_UPDATE_GTT) is no longer
> necessary, disable it.
> 
> My main worry with the MI_UPDATE_GTT are:
> - only used on this one platform so very limited testing coverage
> - async so more opprtunities to screw things up
> - what happens if the engine hangs while we're waiting for MI_UPDATE_GTT
>   to finish?
> - requires working command submission, so even getting a working
>   display now depends on a lot more extra components working correctly
> 
> TODO: MI_UPDATE_GTT might be interesting as an optimization
> though, so perhaps someone should look into always using it
> (assuming the GPU is alive and well)?
> 
> v2: Keep using MI_UPDATE_GTT on VM guests
> v3: use i915_direct_stolen_access()
> 
> Cc: Paz Zcharya <pazz at chromium.org>
> Cc: Nirmoy Das <nirmoy.das at intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Hi Ville,

Thank you so much for this incredible series.
It solves the issue regarding MTL initial plane readout
that Andrzej Hajda and I worked on in
https://patchwork.freedesktop.org/patch/570811/?series=127130&rev=2
In addition, it solved the issue with the new GOP.

I tested it on two different devices with Meteor Lake and it worked perfectly:
no i915 errors, no flickers or observable issues.

Tested-by: Paz Zcharya <pazz at chromium.org>

> ---
>  drivers/gpu/drm/i915/gt/intel_gtt.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c b/drivers/gpu/drm/i915/gt/intel_gtt.c
> index 86f73fe558ca..7811a8c9da06 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
> @@ -24,7 +24,8 @@
>  bool i915_ggtt_require_binder(struct drm_i915_private *i915)
>  {
>  	/* Wa_13010847436 & Wa_14019519902 */
> -	return MEDIA_VER_FULL(i915) == IP_VER(13, 0);
> +	return !i915_direct_stolen_access(i915) &&
> +		MEDIA_VER_FULL(i915) == IP_VER(13, 0);
>  }
>  
>  static bool intel_ggtt_update_needs_vtd_wa(struct drm_i915_private *i915)
> -- 
> 2.43.0
>