[Intel-gfx] [RFC 1/2] drm/i915: Indicate integer up-scaling ratios

[Shashank Sharma]

If the upscaling ratio is a complete integer, Intel display HW can
pickup special scaling mode, which can produce better non-blurry
outputs. This patch adds a check to indicate if this is such an upscaling
opportunity, while calculating the scaler config, and stores it into scaler
state.

Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Daniel Vetter <daniel.vetter at intel.com>
Cc: Vivi, Rodrigo <rodrigo.vivi at intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c  | 21 +++++++++++++++++++
 .../drm/i915/display/intel_display_types.h    |  7 +++++++
 2 files changed, 28 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index ee54d9659c99..613130db3c05 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -5388,6 +5388,19 @@ u16 skl_scaler_calc_phase(int sub, int scale, bool chroma_cosited)
 #define SKL_MIN_YUV_420_SRC_W 16
 #define SKL_MIN_YUV_420_SRC_H 16
 
+static inline bool
+scaling_ratio_integer(int src_w, int dst_w, int src_h, int dst_h)
+{
+	/* Integer mode scaling is applicable only for upscaling scenarios */
+	if (dst_w < src_w || dst_h < src_h)
+		return false;
+
+	if (dst_w % src_w == 0 && dst_h % src_h == 0)
+		return true;
+
+	return false;
+}
+
 static int
 skl_update_scaler(struct intel_crtc_state *crtc_state, bool force_detach,
 		  unsigned int scaler_user, int *scaler_id,
@@ -5422,6 +5435,14 @@ skl_update_scaler(struct intel_crtc_state *crtc_state, bool force_detach,
 		return -EINVAL;
 	}
 
+	/*
+	 * If we are upscaling, and the scaling ratios are integer, we can
+	 * pick nearest-neighbour method in HW for scaling, which produces
+	 * blurless outputs in such scenarios.
+	 */
+	if (scaling_ratio_integer(src_w, dst_w, src_h, dst_h))
+		scaler_state->integer_scaling = true;
+
 	/*
 	 * if plane is being disabled or scaler is no more required or force detach
 	 *  - free scaler binded to this plane/crtc
diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 3c1a5f3e1d22..6bb32fbf3153 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -613,6 +613,13 @@ struct intel_crtc_scaler_state {
 
 	/* scaler used by crtc for panel fitting purpose */
 	int scaler_id;
+
+	/*
+	 * Nearest-neighbor method of upscaling gieves blurless output if
+	 * the upscaling ratio is a complete integer. This bool is to indicate
+	 * such an opportunity.
+	 */
+	bool integer_scaling;
 };
 
 /* drm_mode->private_flags */
-- 
2.17.1