Re: [PATCH 05/11] drm/i915: Extract intel_plane_needs_low_address()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 16 Apr 2026, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Extract the naked "gmch? -> need a low ggtt address" check into
> a more descriptive helper (intel_plane_needs_low_address()).
> The goal being to eliminate all display specific stuff from the
> low level pinning code.
>
> The actual implementation still abuses PIN_MAPPABLE to achieve
> this goal. I'm not entire convinced that this whole thing even
> needs to exist, and the original issue wasn't just caused by
> some other bug. But no time to dig into it right now, so let's
> keep going.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_plane.c | 13 +++++++++++++
>  drivers/gpu/drm/i915/display/intel_plane.h |  2 ++
>  drivers/gpu/drm/i915/i915_fb_pin.c         | 11 ++---------
>  3 files changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_plane.c b/drivers/gpu/drm/i915/display/intel_plane.c
> index f15dd9e91243..f41f4c2ac320 100644
> --- a/drivers/gpu/drm/i915/display/intel_plane.c
> +++ b/drivers/gpu/drm/i915/display/intel_plane.c
> @@ -171,6 +171,19 @@ intel_plane_destroy_state(struct drm_plane *plane,
>  	kfree(plane_state);
>  }
>  
> +bool intel_plane_needs_low_address(struct intel_display *display)
> +{
> +	/*
> +	 * Valleyview is definitely limited to scanning out the first
> +	 * 512MiB. Lets presume this behaviour was inherited from the
> +	 * g4x display engine and that all earlier gen are similarly
> +	 * limited. Testing suggests that it is a little more
> +	 * complicated than this. For example, Cherryview appears quite
> +	 * happy to scanout from anywhere within its global aperture.
> +	 */
> +	return HAS_GMCH(display);
> +}
> +
>  bool intel_plane_needs_physical(struct intel_plane *plane)
>  {
>  	struct intel_display *display = to_intel_display(plane);
> diff --git a/drivers/gpu/drm/i915/display/intel_plane.h b/drivers/gpu/drm/i915/display/intel_plane.h
> index 5a8f2f3baab5..7fa7fbbb58dc 100644
> --- a/drivers/gpu/drm/i915/display/intel_plane.h
> +++ b/drivers/gpu/drm/i915/display/intel_plane.h
> @@ -15,6 +15,7 @@ struct drm_rect;
>  struct intel_atomic_state;
>  struct intel_crtc;
>  struct intel_crtc_state;
> +struct intel_display;
>  struct intel_dsb;
>  struct intel_plane;
>  struct intel_plane_state;
> @@ -79,6 +80,7 @@ int intel_plane_check_src_coordinates(struct intel_plane_state *plane_state);
>  void intel_plane_set_invisible(struct intel_crtc_state *crtc_state,
>  			       struct intel_plane_state *plane_state);
>  void intel_plane_helper_add(struct intel_plane *plane);
> +bool intel_plane_needs_low_address(struct intel_display *display);
>  bool intel_plane_needs_physical(struct intel_plane *plane);
>  void intel_plane_init_cursor_vblank_work(struct intel_plane_state *old_plane_state,
>  					 struct intel_plane_state *new_plane_state);
> diff --git a/drivers/gpu/drm/i915/i915_fb_pin.c b/drivers/gpu/drm/i915/i915_fb_pin.c
> index 96ffc4b0d809..a3e5107c12f0 100644
> --- a/drivers/gpu/drm/i915/i915_fb_pin.c
> +++ b/drivers/gpu/drm/i915/i915_fb_pin.c
> @@ -140,16 +140,9 @@ intel_fb_pin_to_ggtt(const struct drm_framebuffer *fb,
>  
>  	atomic_inc(&i915->pending_fb_pin);
>  
> -	/*
> -	 * Valleyview is definitely limited to scanning out the first
> -	 * 512MiB. Lets presume this behaviour was inherited from the
> -	 * g4x display engine and that all earlier gen are similarly
> -	 * limited. Testing suggests that it is a little more
> -	 * complicated than this. For example, Cherryview appears quite
> -	 * happy to scanout from anywhere within its global aperture.
> -	 */
>  	pinctl = 0;
> -	if (HAS_GMCH(display))
> +	/* PIN_MAPPABLE limits the address to GMADR size */
> +	if (intel_plane_needs_low_address(display))
>  		pinctl |= PIN_MAPPABLE;
>  
>  	i915_gem_ww_ctx_init(&ww, true);

-- 
Jani Nikula, Intel