drm/vkms: Use s32 for internal color pipeline precision

Certain operations require us to preserve values below 0.0 and
above 1.0 (0x0 and 0xffff respectively in 16 bpc unorm). One
such operation is a BT709 encoding operation followed by its
decoding operation, or the reverse.

We'll use s32 values as intermediate in and outputs of our
color operations, for the operations where it matters.

For now this won't apply to LUT operations. We might want to
update those to work on s32 as well, but it's unclear how
that should work for unorm LUT definitions. We'll revisit
that once we add LUT + CTM tests.

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patch.msgid.link/20251115000237.3561250-20-alex.hung@amd.com

diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
index 82116e283e6aa17b909dca220c7bb429a32be0e7..3c1ec430f509602826bb5b835ed76749e0d362b0 100644 (file)
--- a/drivers/gpu/drm/vkms/vkms_composer.c
+++ b/drivers/gpu/drm/vkms/vkms_composer.c
@@ -128,7 +128,7 @@ static void apply_lut(const struct vkms_crtc_state *crtc_state, struct line_buff
        }
 }
 
-static void apply_colorop(struct pixel_argb_u16 *pixel, struct drm_colorop *colorop)
+static void apply_colorop(struct pixel_argb_s32 *pixel, struct drm_colorop *colorop)
 {
        struct drm_colorop_state *colorop_state = colorop->state;
        struct drm_device *dev = colorop->dev;
@@ -157,9 +157,26 @@ static void apply_colorop(struct pixel_argb_u16 *pixel, struct drm_colorop *colo
 static void pre_blend_color_transform(const struct vkms_plane_state *plane_state,
                                      struct line_buffer *output_buffer)
 {
+       struct pixel_argb_s32 pixel;
+
        for (size_t x = 0; x < output_buffer->n_pixels; x++) {
                struct drm_colorop *colorop = plane_state->base.base.color_pipeline;
 
+               /*
+                * Some operations, such as applying a BT709 encoding matrix,
+                * followed by a decoding matrix, require that we preserve
+                * values above 1.0 and below 0.0 until the end of the pipeline.
+                *
+                * Pack the 16-bit UNORM values into s32 to give us head-room to
+                * avoid clipping until we're at the end of the pipeline. Clip
+                * intentionally at the end of the pipeline before packing
+                * UNORM values back into u16.
+                */
+               pixel.a = output_buffer->pixels[x].a;
+               pixel.r = output_buffer->pixels[x].r;
+               pixel.g = output_buffer->pixels[x].g;
+               pixel.b = output_buffer->pixels[x].b;
+
                while (colorop) {
                        struct drm_colorop_state *colorop_state;
 
@@ -169,10 +186,16 @@ static void pre_blend_color_transform(const struct vkms_plane_state *plane_state
                                return;
 
                        if (!colorop_state->bypass)
-                               apply_colorop(&output_buffer->pixels[x], colorop);
+                               apply_colorop(&pixel, colorop);
 
                        colorop = colorop->next;
                }
+
+               /* clamp values */
+               output_buffer->pixels[x].a = clamp_val(pixel.a, 0, 0xffff);
+               output_buffer->pixels[x].r = clamp_val(pixel.r, 0, 0xffff);
+               output_buffer->pixels[x].g = clamp_val(pixel.g, 0, 0xffff);
+               output_buffer->pixels[x].b = clamp_val(pixel.b, 0, 0xffff);
        }
 }
 

diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
index b4e5e4b9958f4b885caad65e9cde547bcd998ad6..0933e4ce0ff03150c8e3fdb54867549c5e90d656 100644 (file)
--- a/drivers/gpu/drm/vkms/vkms_drv.h
+++ b/drivers/gpu/drm/vkms/vkms_drv.h
@@ -45,6 +45,10 @@ struct vkms_frame_info {
        unsigned int rotation;
 };
 
+struct pixel_argb_s32 {
+       s32 a, r, g, b;
+};
+
 /**
  * struct pixel_argb_u16 - Internal representation of a pixel color.
  * @a: Alpha component value, stored in 16 bits, without padding, using