[PATCH] drm/imx/dcss: allow using nearest neighbor interpolation scaling

[Laurentiu Palcu]

This patch adds support for using NN interpolation scaling by setting the
SCALING_FILTER plane property to 1. Otherwise, the default method is used.

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@xxxxxxxxxxx>
---
I had no retro pixel art games to test this with, so I used modetest to see the
results:

To test, I used a 240x135 buffer, upscaled 8 times to 1920x1080:
 * default scaling method using gaussian filter:
/usr/bin/modetest -M imx-dcss -w 33:SCALING_FILTER:0 -P 33@38:240x135*8@XR24
 * NN interpolation method:
/usr/bin/modetest -M imx-dcss -w 33:SCALING_FILTER:1 -P 33@38:240x135*8@XR24

Thanks,
laurentiu

 drivers/gpu/drm/imx/dcss/dcss-dev.h    |  3 ++
 drivers/gpu/drm/imx/dcss/dcss-plane.c  | 10 +++++-
 drivers/gpu/drm/imx/dcss/dcss-scaler.c | 47 +++++++++++++++++++++-----
 3 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/imx/dcss/dcss-dev.h b/drivers/gpu/drm/imx/dcss/dcss-dev.h
index c642ae17837f..1e582270c6ea 100644
--- a/drivers/gpu/drm/imx/dcss/dcss-dev.h
+++ b/drivers/gpu/drm/imx/dcss/dcss-dev.h
@@ -7,6 +7,7 @@
 #define __DCSS_PRV_H__
 
 #include <drm/drm_fourcc.h>
+#include <drm/drm_plane.h>
 #include <linux/io.h>
 #include <video/videomode.h>
 
@@ -165,6 +166,8 @@ void dcss_ss_sync_set(struct dcss_ss *ss, struct videomode *vm,
 /* SCALER */
 int dcss_scaler_init(struct dcss_dev *dcss, unsigned long scaler_base);
 void dcss_scaler_exit(struct dcss_scaler *scl);
+void dcss_scaler_set_filter(struct dcss_scaler *scl, int ch_num,
+			    enum drm_scaling_filter scaling_filter);
 void dcss_scaler_setup(struct dcss_scaler *scl, int ch_num,
 		       const struct drm_format_info *format,
 		       int src_xres, int src_yres, int dst_xres, int dst_yres,
diff --git a/drivers/gpu/drm/imx/dcss/dcss-plane.c b/drivers/gpu/drm/imx/dcss/dcss-plane.c
index 5db093aada2f..03ba88f7f995 100644
--- a/drivers/gpu/drm/imx/dcss/dcss-plane.c
+++ b/drivers/gpu/drm/imx/dcss/dcss-plane.c
@@ -257,7 +257,8 @@ static bool dcss_plane_needs_setup(struct drm_plane_state *state,
 	       state->src_h  != old_state->src_h  ||
 	       fb->format->format != old_fb->format->format ||
 	       fb->modifier  != old_fb->modifier ||
-	       state->rotation != old_state->rotation;
+	       state->rotation != old_state->rotation ||
+	       state->scaling_filter != old_state->scaling_filter;
 }
 
 static void dcss_plane_atomic_update(struct drm_plane *plane,
@@ -313,6 +314,9 @@ static void dcss_plane_atomic_update(struct drm_plane *plane,
 	is_rotation_90_or_270 = state->rotation & (DRM_MODE_ROTATE_90 |
 						   DRM_MODE_ROTATE_270);
 
+	dcss_scaler_set_filter(dcss->scaler, dcss_plane->ch_num,
+			       state->scaling_filter);
+
 	dcss_scaler_setup(dcss->scaler, dcss_plane->ch_num,
 			  state->fb->format,
 			  is_rotation_90_or_270 ? src_h : src_w,
@@ -394,6 +398,10 @@ struct dcss_plane *dcss_plane_init(struct drm_device *drm,
 	if (ret)
 		return ERR_PTR(ret);
 
+	drm_plane_create_scaling_filter_property(&dcss_plane->base,
+					BIT(DRM_SCALING_FILTER_DEFAULT) |
+					BIT(DRM_SCALING_FILTER_NEAREST_NEIGHBOR));
+
 	drm_plane_create_rotation_property(&dcss_plane->base,
 					   DRM_MODE_ROTATE_0,
 					   DRM_MODE_ROTATE_0   |
diff --git a/drivers/gpu/drm/imx/dcss/dcss-scaler.c b/drivers/gpu/drm/imx/dcss/dcss-scaler.c
index cd21905de580..47852b9dd5ea 100644
--- a/drivers/gpu/drm/imx/dcss/dcss-scaler.c
+++ b/drivers/gpu/drm/imx/dcss/dcss-scaler.c
@@ -77,6 +77,8 @@ struct dcss_scaler_ch {
 
 	u32 c_vstart;
 	u32 c_hstart;
+
+	bool use_nn_interpolation;
 };
 
 struct dcss_scaler {
@@ -243,6 +245,17 @@ static void dcss_scaler_gaussian_filter(int fc_q, bool use_5_taps,
 	}
 }
 
+static void dcss_scaler_nearest_neighbor_filter(bool use_5_taps,
+						int coef[][PSC_NUM_TAPS])
+{
+	int i, j;
+
+	for (i = 0; i < PSC_STORED_PHASES; i++)
+		for (j = 0; j < PSC_NUM_TAPS; j++)
+			coef[i][j] = j == PSC_NUM_TAPS >> 1 ?
+						(1 << PSC_COEFF_PRECISION) : 0;
+}
+
 /**
  * dcss_scaler_filter_design() - Compute filter coefficients using
  *				 Gaussian filter.
@@ -253,7 +266,8 @@ static void dcss_scaler_gaussian_filter(int fc_q, bool use_5_taps,
  */
 static void dcss_scaler_filter_design(int src_length, int dst_length,
 				      bool use_5_taps, bool phase0_identity,
-				      int coef[][PSC_NUM_TAPS])
+				      int coef[][PSC_NUM_TAPS],
+				      bool nn_interpolation)
 {
 	int fc_q;
 
@@ -263,8 +277,11 @@ static void dcss_scaler_filter_design(int src_length, int dst_length,
 	else
 		fc_q = div_q(dst_length, src_length * PSC_NUM_PHASES);
 
-	/* compute gaussian filter coefficients */
-	dcss_scaler_gaussian_filter(fc_q, use_5_taps, phase0_identity, coef);
+	if (nn_interpolation)
+		dcss_scaler_nearest_neighbor_filter(use_5_taps, coef);
+	else
+		/* compute gaussian filter coefficients */
+		dcss_scaler_gaussian_filter(fc_q, use_5_taps, phase0_identity, coef);
 }
 
 static void dcss_scaler_write(struct dcss_scaler_ch *ch, u32 val, u32 ofs)
@@ -653,12 +670,14 @@ static void dcss_scaler_yuv_coef_set(struct dcss_scaler_ch *ch,
 
 	/* horizontal luma */
 	dcss_scaler_filter_design(src_xres, dst_xres, false,
-				  src_xres == dst_xres, coef);
+				  src_xres == dst_xres, coef,
+				  ch->use_nn_interpolation);
 	dcss_scaler_program_7_coef_set(ch, DCSS_SCALER_COEF_HLUM, coef);
 
 	/* vertical luma */
 	dcss_scaler_filter_design(src_yres, dst_yres, program_5_taps,
-				  src_yres == dst_yres, coef);
+				  src_yres == dst_yres, coef,
+				  ch->use_nn_interpolation);
 
 	if (program_5_taps)
 		dcss_scaler_program_5_coef_set(ch, DCSS_SCALER_COEF_VLUM, coef);
@@ -678,14 +697,14 @@ static void dcss_scaler_yuv_coef_set(struct dcss_scaler_ch *ch,
 	/* horizontal chroma */
 	dcss_scaler_filter_design(src_xres, dst_xres, false,
 				  (src_xres == dst_xres) && (ch->c_hstart == 0),
-				  coef);
+				  coef, ch->use_nn_interpolation);
 
 	dcss_scaler_program_7_coef_set(ch, DCSS_SCALER_COEF_HCHR, coef);
 
 	/* vertical chroma */
 	dcss_scaler_filter_design(src_yres, dst_yres, program_5_taps,
 				  (src_yres == dst_yres) && (ch->c_vstart == 0),
-				  coef);
+				  coef, ch->use_nn_interpolation);
 	if (program_5_taps)
 		dcss_scaler_program_5_coef_set(ch, DCSS_SCALER_COEF_VCHR, coef);
 	else
@@ -700,12 +719,14 @@ static void dcss_scaler_rgb_coef_set(struct dcss_scaler_ch *ch,
 
 	/* horizontal RGB */
 	dcss_scaler_filter_design(src_xres, dst_xres, false,
-				  src_xres == dst_xres, coef);
+				  src_xres == dst_xres, coef,
+				  ch->use_nn_interpolation);
 	dcss_scaler_program_7_coef_set(ch, DCSS_SCALER_COEF_HLUM, coef);
 
 	/* vertical RGB */
 	dcss_scaler_filter_design(src_yres, dst_yres, false,
-				  src_yres == dst_yres, coef);
+				  src_yres == dst_yres, coef,
+				  ch->use_nn_interpolation);
 	dcss_scaler_program_7_coef_set(ch, DCSS_SCALER_COEF_VLUM, coef);
 }
 
@@ -751,6 +772,14 @@ static void dcss_scaler_set_rgb10_order(struct dcss_scaler_ch *ch,
 	ch->sdata_ctrl |= a2r10g10b10_format << A2R10G10B10_FORMAT_POS;
 }
 
+void dcss_scaler_set_filter(struct dcss_scaler *scl, int ch_num,
+			    enum drm_scaling_filter scaling_filter)
+{
+	struct dcss_scaler_ch *ch = &scl->ch[ch_num];
+
+	ch->use_nn_interpolation = scaling_filter == DRM_SCALING_FILTER_NEAREST_NEIGHBOR;
+}
+
 void dcss_scaler_setup(struct dcss_scaler *scl, int ch_num,
 		       const struct drm_format_info *format,
 		       int src_xres, int src_yres, int dst_xres, int dst_yres,
-- 
2.23.0