[RFC][PATCH 5/5] drm/i915/display: Add Nearest-neighbor based integer scaling support

[Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>]

Integer scaling (IS) is a nearest-neighbor upscaling technique that
simply scales up the existing pixels by an integer
(i.e., whole number) multiplier.Nearest-neighbor (NN) interpolation
works by filling in the missing color values in the upscaled image
with that of the coordinate-mapped nearest source pixel value.

Both IS and NN preserve the clarity of the original image. Integer
scaling is particularly useful for pixel art games that rely on
sharp, blocky images to deliver their distinctive look.

Program the scaler filter coefficients to enable the NN filter if
scaling filter property is set to DRM_SCALING_FILTER_NEAREST_NEIGHBOR
and enable integer scaling.

Bspec: 49247

Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 83 +++++++++++++++++++-
 drivers/gpu/drm/i915/display/intel_display.h |  2 +
 drivers/gpu/drm/i915/display/intel_sprite.c  | 20 +++--
 3 files changed, 97 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index b5903ef3c5a0..6d5f59203258 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -6237,6 +6237,73 @@ void skl_scaler_disable(const struct intel_crtc_state *old_crtc_state)
 		skl_detach_scaler(crtc, i);
 }
 
+/**
+ *  Theory behind setting nearest-neighbor integer scaling:
+ *
+ *  17 phase of 7 taps requires 119 coefficients in 60 dwords per set.
+ *  The letter represents the filter tap (D is the center tap) and the number
+ *  represents the coefficient set for a phase (0-16).
+ *
+ *         +------------+------------------------+------------------------+
+ *         |Index value | Data value coeffient 1 | Data value coeffient 2 |
+ *         +------------+------------------------+------------------------+
+ *         |   00h      |          B0            |          A0            |
+ *         +------------+------------------------+------------------------+
+ *         |   01h      |          D0            |          C0            |
+ *         +------------+------------------------+------------------------+
+ *         |   02h      |          F0            |          E0            |
+ *         +------------+------------------------+------------------------+
+ *         |   03h      |          A1            |          G0            |
+ *         +------------+------------------------+------------------------+
+ *         |   04h      |          C1            |          B1            |
+ *         +------------+------------------------+------------------------+
+ *         |   ...      |          ...           |          ...           |
+ *         +------------+------------------------+------------------------+
+ *         |   38h      |          B16           |          A16           |
+ *         +------------+------------------------+------------------------+
+ *         |   39h      |          D16           |          C16           |
+ *         +------------+------------------------+------------------------+
+ *         |   3Ah      |          F16           |          C16           |
+ *         +------------+------------------------+------------------------+
+ *         |   3Bh      |        Reserved        |          G16           |
+ *         +------------+------------------------+------------------------+
+ *
+ *  To enable nearest-neighbor scaling:  program scaler coefficents with
+ *  the center tap (Dxx) values set to 1 and all other values set to 0 as per
+ *  SCALER_COEFFICIENT_FORMAT
+ *
+ */
+void skl_setup_nearest_neighbor_filter(struct drm_i915_private *dev_priv,
+				  enum pipe pipe, int scaler_id)
+{
+
+	int coeff = 0;
+	int phase = 0;
+	int tap;
+	int val = 0;
+
+	/*enable the index auto increment.*/
+	intel_de_write_fw(dev_priv, SKL_PS_COEF_INDEX_SET0(pipe, scaler_id),
+			  _PS_COEE_INDEX_AUTO_INC);
+
+	for (phase = 0; phase < 17; phase++) {
+		for (tap = 0; tap < 7; tap++) {
+			coeff++;
+			if (tap == 3)
+				val = (phase % 2) ? (0x800) : (0x800 << 16);
+
+			if (coeff % 2 == 0) {
+				intel_de_write_fw(dev_priv, SKL_PS_COEF_DATA_SET0(pipe, scaler_id), val);
+				val = 0;
+			}
+
+		}
+
+	}
+
+	intel_de_write_fw(dev_priv, SKL_PS_COEF_DATA_SET0(pipe, scaler_id), 0);
+}
+
 static void skl_pfit_enable(const struct intel_crtc_state *crtc_state)
 {
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
@@ -6260,9 +6327,23 @@ static void skl_pfit_enable(const struct intel_crtc_state *crtc_state)
 		pfit_w = (crtc_state->pch_pfit.size >> 16) & 0xFFFF;
 		pfit_h = crtc_state->pch_pfit.size & 0xFFFF;
 
+		id = scaler_state->scaler_id;
+
 		if (state->scaling_filter ==
 		    DRM_SCALING_FILTER_NEAREST_NEIGHBOR) {
 			scaling_filter = PS_FILTER_PROGRAMMED;
+			skl_setup_nearest_neighbor_filter(dev_priv, pipe, id);
+
+			/* Make the scaling window size to integer multiple of
+			 * source.
+			 *
+			 * TODO: Should userspace take desision to round
+			 * scaling window to integer multiple?
+			 */
+			pfit_w = rounddown(pfit_w,
+					   (crtc_state->pipe_src_w << 16));
+			pfit_h = rounddown(pfit_h,
+					   (crtc_state->pipe_src_h << 16));
 		}
 
 		hscale = (crtc_state->pipe_src_w << 16) / pfit_w;
@@ -6271,8 +6352,6 @@ static void skl_pfit_enable(const struct intel_crtc_state *crtc_state)
 		uv_rgb_hphase = skl_scaler_calc_phase(1, hscale, false);
 		uv_rgb_vphase = skl_scaler_calc_phase(1, vscale, false);
 
-		id = scaler_state->scaler_id;
-
 		spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
 
 		intel_de_write_fw(dev_priv, SKL_PS_CTRL(pipe, id),
diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
index f92efbbec838..49f58d3c98fe 100644
--- a/drivers/gpu/drm/i915/display/intel_display.h
+++ b/drivers/gpu/drm/i915/display/intel_display.h
@@ -586,6 +586,8 @@ void intel_crtc_arm_fifo_underrun(struct intel_crtc *crtc,
 u16 skl_scaler_calc_phase(int sub, int scale, bool chroma_center);
 int skl_update_scaler_crtc(struct intel_crtc_state *crtc_state);
 void skl_scaler_disable(const struct intel_crtc_state *old_crtc_state);
+void skl_setup_nearest_neighbor_filter(struct drm_i915_private *dev_priv,
+				  enum pipe pipe, int scaler_id);
 void ilk_pfit_disable(const struct intel_crtc_state *old_crtc_state);
 u32 glk_plane_color_ctl(const struct intel_crtc_state *crtc_state,
 			const struct intel_plane_state *plane_state);
diff --git a/drivers/gpu/drm/i915/display/intel_sprite.c b/drivers/gpu/drm/i915/display/intel_sprite.c
index fd7b31a21723..5bef5c031374 100644
--- a/drivers/gpu/drm/i915/display/intel_sprite.c
+++ b/drivers/gpu/drm/i915/display/intel_sprite.c
@@ -415,18 +415,26 @@ skl_program_scaler(struct intel_plane *plane,
 	u16 y_vphase, uv_rgb_vphase;
 	int hscale, vscale;
 	const struct drm_plane_state *state = &plane_state->uapi;
+	u32 src_w = drm_rect_width(&plane_state->uapi.src) >> 16;
+	u32 src_h = drm_rect_height(&plane_state->uapi.src) >> 16;
 	u32 scaling_filter = PS_FILTER_MEDIUM;
+	struct drm_rect dst;
 
 	if (state->scaling_filter == DRM_SCALING_FILTER_NEAREST_NEIGHBOR) {
 		scaling_filter = PS_FILTER_PROGRAMMED;
+		skl_setup_nearest_neighbor_filter(dev_priv, pipe, scaler_id);
+
+		/* Make the scaling window size to integer multiple of source
+		 * TODO: Should userspace take desision to round scaling window
+		 * to integer multiple?
+		 */
+		crtc_w = rounddown(crtc_w, src_w);
+		crtc_h = rounddown(crtc_h, src_h);
 	}
 
-	hscale = drm_rect_calc_hscale(&plane_state->uapi.src,
-				      &plane_state->uapi.dst,
-				      0, INT_MAX);
-	vscale = drm_rect_calc_vscale(&plane_state->uapi.src,
-				      &plane_state->uapi.dst,
-				      0, INT_MAX);
+	drm_rect_init(&dst, crtc_x, crtc_y, crtc_w, crtc_h);
+	hscale = drm_rect_calc_hscale(&plane_state->uapi.src, &dst, 0, INT_MAX);
+	vscale = drm_rect_calc_vscale(&plane_state->uapi.src, &dst, 0, INT_MAX);
 
 	/* TODO: handle sub-pixel coordinates */
 	if (intel_format_info_is_yuv_semiplanar(fb->format, fb->modifier) &&
-- 
2.23.0