Message-Id: <20240223-yuv-v2-5-aa6be2827bb7@bootlin.com>
Date: Fri, 23 Feb 2024 12:37:25 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>, 
 Melissa Wen <melissa.srw@...il.com>, 
 Maíra Canal <mairacanal@...eup.net>, 
 Haneen Mohammed <hamohammed.sa@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, arthurgrillo@...eup.net, 
 Jonathan Corbet <corbet@....net>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 jeremie.dautheribes@...tlin.com, miquel.raynal@...tlin.com, 
 thomas.petazzoni@...tlin.com, Louis Chauvet <louis.chauvet@...tlin.com>
Subject: [PATCH v2 5/9] drm/vkms: Re-introduce line-per-line composition
 algorithm

Re-introduce a line-by-line composition algorithm for each pixel format.
This allows more performance by not requiring an indirection per pixel
read. This patch is focussed on readability of the code.

Line-by-line composition was introduced by [1] but rewritten back to
pixel-by-pixel algorithm in [2]. At this time, nobody noticed the impact
on performance, and it was merged.

This patch is almost a revert of [2], but in addition efforts have been
made to increase readability and maintenability of the rotation handling.
The blend function is now divided in two parts:
- Transformation of coordinates from the output referential to the source
referential
- Line conversion and blending

Most of the complexity of the rotation management is avoided by using
drm_rect_* helpers. The remaning complexity is around the clipping, to
avoid reading/writing oudside source/destination buffers.

The pixel conversion is now done line-by-line, so the read_pixel_t was
replaced with read_pixel_line_t callback. This way the indirection is only
required once per line and per plane, instead of once per pixel and per
plane.

The read_line_t callbacks are very similar for most pixel format, but it
is required to avoid performance impact. Some helpers were created to
avoid code repetition:
- get_step_1x1: get the step in byte to reach next pixel block in a
  certain direction
- *_to_argb_u16: helpers to perform colors conversion. They should be
  inlined by the compiler, and they are used to avoid repetition between
  multiple variants of the same format (argb/xrgb and maybe in the
  future for formats like bgr formats).

This new algorithm was tested with:
- kms_plane (for color conversions)
- kms_rotation_crc (for rotations of planes)
- kms_cursor_crc (for translations of planes)
The performance gain was mesured with:
- kms_fb_stress

[1]: commit 8ba1648567e2 ("drm: vkms: Refactor the plane composer to accept
     new formats")
     https://lore.kernel.org/all/20220905190811.25024-7-igormtorrente@gmail.com/
[2]: commit 322d716a3e8a ("drm/vkms: isolate pixel conversion
     functionality")
     https://lore.kernel.org/all/20230418130525.128733-2-mcanal@igalia.com/

Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
---
 drivers/gpu/drm/vkms/vkms_composer.c | 219 +++++++++++++++++++++++-------
 drivers/gpu/drm/vkms/vkms_drv.h      |  25 +++-
 drivers/gpu/drm/vkms/vkms_formats.c  | 253 ++++++++++++++++++++++-------------
 drivers/gpu/drm/vkms/vkms_formats.h  |   2 +-
 drivers/gpu/drm/vkms/vkms_plane.c    |   8 +-
 5 files changed, 350 insertions(+), 157 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
index 5b341222d239..e555bf9c1aee 100644
--- a/drivers/gpu/drm/vkms/vkms_composer.c
+++ b/drivers/gpu/drm/vkms/vkms_composer.c
@@ -24,9 +24,10 @@ static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)
 
 /**
  * pre_mul_alpha_blend - alpha blending equation
- * @frame_info: Source framebuffer's metadata
  * @stage_buffer: The line with the pixels from src_plane
  * @output_buffer: A line buffer that receives all the blends output
+ * @x_start: The start offset to avoid useless copy
+ * @count: The number of byte to copy
  *
  * Using the information from the `frame_info`, this blends only the
  * necessary pixels from the `stage_buffer` to the `output_buffer`
@@ -37,51 +38,23 @@ static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)
  * drm_plane_create_blend_mode_property(). Also, this formula assumes a
  * completely opaque background.
  */
-static void pre_mul_alpha_blend(struct vkms_frame_info *frame_info,
-				struct line_buffer *stage_buffer,
-				struct line_buffer *output_buffer)
+static void pre_mul_alpha_blend(
+	struct line_buffer *stage_buffer,
+	struct line_buffer *output_buffer,
+	int x_start,
+	int pixel_count)
 {
-	int x_dst = frame_info->dst.x1;
-	struct pixel_argb_u16 *out = output_buffer->pixels + x_dst;
-	struct pixel_argb_u16 *in = stage_buffer->pixels;
-	int x_limit = min_t(size_t, drm_rect_width(&frame_info->dst),
-			    stage_buffer->n_pixels);
-
-	for (int x = 0; x < x_limit; x++) {
-		out[x].a = (u16)0xffff;
-		out[x].r = pre_mul_blend_channel(in[x].r, out[x].r, in[x].a);
-		out[x].g = pre_mul_blend_channel(in[x].g, out[x].g, in[x].a);
-		out[x].b = pre_mul_blend_channel(in[x].b, out[x].b, in[x].a);
+	struct pixel_argb_u16 *out = &output_buffer->pixels[x_start];
+	struct pixel_argb_u16 *in = &stage_buffer->pixels[x_start];
+
+	for (int i = 0; i < pixel_count; i++) {
+		out[i].a = (u16)0xffff;
+		out[i].r = pre_mul_blend_channel(in[i].r, out[i].r, in[i].a);
+		out[i].g = pre_mul_blend_channel(in[i].g, out[i].g, in[i].a);
+		out[i].b = pre_mul_blend_channel(in[i].b, out[i].b, in[i].a);
 	}
 }
 
-static int get_y_pos(struct vkms_frame_info *frame_info, int y)
-{
-	if (frame_info->rotation & DRM_MODE_REFLECT_Y)
-		return drm_rect_height(&frame_info->rotated) - y - 1;
-
-	switch (frame_info->rotation & DRM_MODE_ROTATE_MASK) {
-	case DRM_MODE_ROTATE_90:
-		return frame_info->rotated.x2 - y - 1;
-	case DRM_MODE_ROTATE_270:
-		return y + frame_info->rotated.x1;
-	default:
-		return y;
-	}
-}
-
-static bool check_limit(struct vkms_frame_info *frame_info, int pos)
-{
-	if (drm_rotation_90_or_270(frame_info->rotation)) {
-		if (pos >= 0 && pos < drm_rect_width(&frame_info->rotated))
-			return true;
-	} else {
-		if (pos >= frame_info->rotated.y1 && pos < frame_info->rotated.y2)
-			return true;
-	}
-
-	return false;
-}
 
 static void fill_background(const struct pixel_argb_u16 *background_color,
 			    struct line_buffer *output_buffer)
@@ -163,6 +136,37 @@ static void apply_lut(const struct vkms_crtc_state *crtc_state, struct line_buff
 	}
 }
 
+/**
+ * direction_for_rotation() - Helper to get the correct reading direction for a specific rotation
+ *
+ * @rotation: rotation to analyze
+ */
+enum pixel_read_direction direction_for_rotation(unsigned int rotation)
+{
+	if (rotation & DRM_MODE_ROTATE_0) {
+		if (rotation & DRM_MODE_REFLECT_X)
+			return READ_LEFT;
+		else
+			return READ_RIGHT;
+	} else if (rotation & DRM_MODE_ROTATE_90) {
+		if (rotation & DRM_MODE_REFLECT_Y)
+			return READ_UP;
+		else
+			return READ_DOWN;
+	} else if (rotation & DRM_MODE_ROTATE_180) {
+		if (rotation & DRM_MODE_REFLECT_X)
+			return READ_RIGHT;
+		else
+			return READ_LEFT;
+	} else if (rotation & DRM_MODE_ROTATE_270) {
+		if (rotation & DRM_MODE_REFLECT_Y)
+			return READ_DOWN;
+		else
+			return READ_UP;
+	}
+	return READ_RIGHT;
+}
+
 /**
  * blend - blend the pixels from all planes and compute crc
  * @wb: The writeback frame buffer metadata
@@ -183,11 +187,11 @@ static void blend(struct vkms_writeback_job *wb,
 {
 	struct vkms_plane_state **plane = crtc_state->active_planes;
 	u32 n_active_planes = crtc_state->num_active_planes;
-	int y_pos;
 
 	const struct pixel_argb_u16 background_color = { .a = 0xffff };
 
 	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
+	size_t crtc_x_limit = crtc_state->base.crtc->mode.hdisplay;
 
 	/*
 	 * The planes are composed line-by-line. It is a necessary complexity to avoid poor
@@ -198,22 +202,133 @@ static void blend(struct vkms_writeback_job *wb,
 
 		/* The active planes are composed associatively in z-order. */
 		for (size_t i = 0; i < n_active_planes; i++) {
-			y_pos = get_y_pos(plane[i]->frame_info, y);
+			struct vkms_plane_state *current_plane = plane[i];
 
-			if (!check_limit(plane[i]->frame_info, y_pos))
+			/* Avoid rendering useless lines */
+			if (y < current_plane->frame_info->dst.y1 ||
+			    y >= current_plane->frame_info->dst.y2) {
 				continue;
-
-			vkms_compose_row(stage_buffer, plane[i], y_pos);
-			pre_mul_alpha_blend(plane[i]->frame_info, stage_buffer,
-					    output_buffer);
+			}
+
+			/*
+			 * src_px is the line to copy. The initial coordinates are inside the
+			 * destination framebuffer, and then drm_rect_* helpers are used to
+			 * compute the correct position into the source framebuffer.
+			 */
+			struct drm_rect src_px = DRM_RECT_INIT(
+				current_plane->frame_info->dst.x1, y,
+				drm_rect_width(&current_plane->frame_info->dst), 1);
+			struct drm_rect tmp_src;
+
+			drm_rect_fp_to_int(&tmp_src, &current_plane->frame_info->src);
+
+			/*
+			 * [1]: Clamping src_px to the crtc_x_limit to avoid writing outside of the
+			 * destination buffer
+			 */
+			src_px.x2 = min_t(int, src_px.x2, (int)crtc_x_limit);
+
+			/*
+			 * Transform the coordinate x/y from the crtc to coordinates into
+			 * coordinates for the src buffer.
+			 *
+			 * - Cancel the offset of the dst buffer.
+			 * - Invert the rotation. This assumes that
+			 *   dst = drm_rect_rotate(src, rotation) (dst and src have the
+			 *   same size, but can be rotated).
+			 * - Apply the offset of the source rectangle to the coordinate.
+			 */
+			drm_rect_translate(&src_px, -current_plane->frame_info->dst.x1,
+					   -current_plane->frame_info->dst.y1);
+			drm_rect_rotate_inv(&src_px,
+					    drm_rect_width(&tmp_src),
+					    drm_rect_height(&tmp_src),
+					    current_plane->frame_info->rotation);
+			drm_rect_translate(&src_px, tmp_src.x1, tmp_src.y1);
+
+			/* Get the correct reading direction in the source buffer. */
+
+			enum pixel_read_direction direction =
+				direction_for_rotation(current_plane->frame_info->rotation);
+
+			int x_start = src_px.x1;
+			int y_start = src_px.y1;
+			int pixel_count;
+			/* [2]: Compute and clamp the number of pixel to read */
+			if (direction == READ_RIGHT || direction == READ_LEFT) {
+				/*
+				 * In horizontal reading, the src_px width is the number of pixel to
+				 * read
+				 */
+				pixel_count = drm_rect_width(&src_px);
+				if (x_start < 0) {
+					pixel_count += x_start;
+					x_start = 0;
+				}
+				if (x_start + pixel_count > current_plane->frame_info->fb->width) {
+					pixel_count =
+						(int)current_plane->frame_info->fb->width - x_start;
+				}
+			} else {
+				/*
+				 * In vertical reading, the src_px height is the number of pixel to
+				 * read
+				 */
+				pixel_count = drm_rect_height(&src_px);
+				if (y_start < 0) {
+					pixel_count += y_start;
+					y_start = 0;
+				}
+				if (y_start + pixel_count > current_plane->frame_info->fb->height) {
+					pixel_count =
+						(int)current_plane->frame_info->fb->width - y_start;
+				}
+			}
+
+			if (pixel_count <= 0) {
+				/* Nothing to read, so avoid multiple function calls for nothing */
+				continue;
+			}
+
+			/*
+			 * Modify the starting point to take in account the rotation
+			 *
+			 * src_px is the top-left corner, so when reading READ_LEFT or READ_TOP, it
+			 * must be changed to the top-right/bottom-left corner.
+			 */
+			if (direction == READ_LEFT) {
+				// x_start is now the right point
+				x_start += pixel_count - 1;
+			} else if (direction == READ_UP) {
+				// y_start is now the bottom point
+				y_start += pixel_count - 1;
+			}
+
+			/*
+			 * Perform the conversion and the blending
+			 *
+			 * Here we know that the read line (x_start, y_start, pixel_count) is
+			 * inside the source buffer [2] and we don't write outside the stage
+			 * buffer [1]
+			 */
+			current_plane->pixel_read_line(
+				current_plane->frame_info,
+				x_start,
+				y_start,
+				direction,
+				pixel_count,
+				&stage_buffer->pixels[current_plane->frame_info->dst.x1]);
+
+			pre_mul_alpha_blend(stage_buffer, output_buffer,
+					    current_plane->frame_info->dst.x1,
+					    pixel_count);
 		}
 
 		apply_lut(crtc_state, output_buffer);
 
 		*crc32 = crc32_le(*crc32, (void *)output_buffer->pixels, row_size);
-
 		if (wb)
-			vkms_writeback_row(wb, output_buffer, y_pos);
+			vkms_writeback_row(wb, output_buffer, y);
 	}
 }
 
@@ -224,7 +339,7 @@ static int check_format_funcs(struct vkms_crtc_state *crtc_state,
 	u32 n_active_planes = crtc_state->num_active_planes;
 
 	for (size_t i = 0; i < n_active_planes; i++)
-		if (!planes[i]->pixel_read)
+		if (!planes[i]->pixel_read_line)
 			return -1;
 
 	if (active_wb && !active_wb->pixel_write)
diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
index 886c885c8cf5..ccc5be009f15 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.h
+++ b/drivers/gpu/drm/vkms/vkms_drv.h
@@ -39,7 +39,6 @@
 struct vkms_frame_info {
 	struct drm_framebuffer *fb;
 	struct drm_rect src, dst;
-	struct drm_rect rotated;
 	struct iosys_map map[DRM_FORMAT_MAX_PLANES];
 	unsigned int rotation;
 };
@@ -69,14 +68,27 @@ struct vkms_writeback_job {
 	pixel_write_t pixel_write;
 };
 
+enum pixel_read_direction {
+	READ_UP,
+	READ_DOWN,
+	READ_LEFT,
+	READ_RIGHT
+};
+
 /**
- * typedef pixel_read_t - These functions are used to read a pixel in the source frame,
+<<<<<<< HEAD
+ * typedef pixel_read_line_t - These functions are used to read a pixel line in the source frame,
  * convert it to `struct pixel_argb_u16` and write it to @out_pixel.
  *
- * @src_pixels: Pointer to the pixel to read
- * @out_pixel: Pointer to write the converted pixel
+ * @frame_info: Frame used as source for the pixel value
+ * @y: Y (height) coordinate in the source buffer
+ * @x_start: X (width) coordinate of the first pixel to copy
+ * @x_end: X (width) coordinate of the last pixel to copy
+ * @out_pixel: Pointer where to write the pixel value. Pixels will be written between x_start and
+ *  x_end.
  */
-typedef void (*pixel_read_t)(u8 *src_pixels, struct pixel_argb_u16 *out_pixel);
+typedef void (*pixel_read_line_t)(struct vkms_frame_info *frame_info, int x_start, int y_start, enum
+	pixel_read_direction direction, int count, struct pixel_argb_u16 out_pixel[]);
 
 /**
  * vkms_plane_state - Driver specific plane state
@@ -88,7 +100,7 @@ typedef void (*pixel_read_t)(u8 *src_pixels, struct pixel_argb_u16 *out_pixel);
 struct vkms_plane_state {
 	struct drm_shadow_plane_state base;
 	struct vkms_frame_info *frame_info;
-	pixel_read_t pixel_read;
+	pixel_read_line_t pixel_read_line;
 };
 
 struct vkms_plane {
@@ -193,7 +205,6 @@ int vkms_verify_crc_source(struct drm_crtc *crtc, const char *source_name,
 /* Composer Support */
 void vkms_composer_worker(struct work_struct *work);
 void vkms_set_composer(struct vkms_output *out, bool enabled);
-void vkms_compose_row(struct line_buffer *stage_buffer, struct vkms_plane_state *plane, int y);
 void vkms_writeback_row(struct vkms_writeback_job *wb, const struct line_buffer *src_buffer, int y);
 
 /* Writeback */
diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
index 1f5aeba57ad6..46daea6d3ee9 100644
--- a/drivers/gpu/drm/vkms/vkms_formats.c
+++ b/drivers/gpu/drm/vkms/vkms_formats.c
@@ -11,21 +11,29 @@
 
 /**
  * packed_pixels_offset() - Get the offset of the block containing the pixel at coordinates x/y
- * in the first plane
  *
  * @frame_info: Buffer metadata
  * @x: The x coordinate of the wanted pixel in the buffer
  * @y: The y coordinate of the wanted pixel in the buffer
+ * @plane_index: The index of the plane to use
  *
  * The caller must be aware that this offset is not always a pointer to a pixel. If individual
  * pixel values are needed, they have to be extracted from the resulting block.
  */
-static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int y)
+static size_t packed_pixels_offset(const struct vkms_frame_info *frame_info, int x, int y,
+				   size_t plane_index)
 {
 	struct drm_framebuffer *fb = frame_info->fb;
-
-	return fb->offsets[0] + (y * fb->pitches[0])
-			      + (x * fb->format->cpp[0]);
+	const struct drm_format_info *format = frame_info->fb->format;
+	/* Directly using x and y to multiply pitches and format->ccp is not sufficient because
+	 * in some formats a block can represent multiple pixels.
+	 *
+	 * Dividing x and y by the block size allows to extract the correct offset of the block
+	 * containing the pixel.
+	 */
+	return fb->offsets[plane_index] +
+	       (y / drm_format_info_block_width(format, plane_index)) * fb->pitches[plane_index] +
+	       (x / drm_format_info_block_height(format, plane_index)) * format->char_per_block[plane_index];
 }
 
 /**
@@ -35,44 +43,56 @@ static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int
  * @frame_info: Buffer metadata
  * @x: The x(width) coordinate inside the plane
  * @y: The y(height) coordinate inside the plane
+ * @plane_index: The index of the plane
  *
- * Takes the information stored in the frame_info, a pair of coordinates, and
- * returns the address of the first color channel.
- * This function assumes the channels are packed together, i.e. a color channel
- * comes immediately after another in the memory. And therefore, this function
- * doesn't work for YUV with chroma subsampling (e.g. YUV420 and NV21).
+ * Takes the information stored in the frame_info, a pair of coordinates, and returns the address
+ * of the block containing this pixel.
+ * The caller must be aware that this pointer is sometimes not directly a pixel, it needs some
+ * additional work to extract pixel color from this block.
  */
 static void *packed_pixels_addr(const struct vkms_frame_info *frame_info,
-				int x, int y)
+				int x, int y, size_t plane_index)
 {
-	size_t offset = pixel_offset(frame_info, x, y);
-
-	return (u8 *)frame_info->map[0].vaddr + offset;
+	return (u8 *)frame_info->map[0].vaddr + packed_pixels_offset(frame_info, x, y, plane_index);
 }
 
-static void *get_packed_src_addr(const struct vkms_frame_info *frame_info, int y)
+/**
+ * get_step_1x1() - Common helper to compute the correct step value between each pixel to read in a
+ * certain direction.
+ * This must be used only with format where blockh == blockw == 1.
+ * In the case when direction is not a valid pixel_read_direction, the returned step is 0, so you
+ * must not rely on this result to create a loop variant.
+ *
+ * @fb Framebuffer to iter on
+ * @direction Direction of the reading
+ */
+static int get_step_1x1(struct drm_framebuffer *fb, enum pixel_read_direction direction,
+			int plane_index)
 {
-	int x_src = frame_info->src.x1 >> 16;
-	int y_src = y - frame_info->rotated.y1 + (frame_info->src.y1 >> 16);
-
-	return packed_pixels_addr(frame_info, x_src, y_src);
+	switch (direction) {
+	default:
+		DRM_ERROR("Invalid direction for pixel reading: %d\n", direction);
+		return 0;
+	case READ_RIGHT:
+		return fb->format->char_per_block[plane_index];
+	case READ_LEFT:
+		return -fb->format->char_per_block[plane_index];
+	case READ_DOWN:
+		return (int)fb->pitches[plane_index];
+	case READ_UP:
+		return -(int)fb->pitches[plane_index];
+	}
 }
 
-static int get_x_position(const struct vkms_frame_info *frame_info, int limit, int x)
-{
-	if (frame_info->rotation & (DRM_MODE_REFLECT_X | DRM_MODE_ROTATE_270))
-		return limit - x - 1;
-	return x;
-}
 
 /*
- * The following  functions take pixel data from the buffer and convert them to the format
+ * The following  functions take pixel data (a, r, g, b, pixel, ...), convert them to the format
  * ARGB16161616 in out_pixel.
  *
- * They are used in the `vkms_compose_row` function to handle multiple formats.
+ * They are used in the `read_line`s functions to avoid duplicate work for some pixel formats.
  */
 
-static void ARGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
+static void ARGB8888_to_argb_u16(struct pixel_argb_u16 *out_pixel, int a, int r, int g, int b)
 {
 	/*
 	 * The 257 is the "conversion ratio". This number is obtained by the
@@ -80,48 +100,26 @@ static void ARGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixe
 	 * the best color value in a pixel format with more possibilities.
 	 * A similar idea applies to others RGB color conversions.
 	 */
-	out_pixel->a = (u16)src_pixels[3] * 257;
-	out_pixel->r = (u16)src_pixels[2] * 257;
-	out_pixel->g = (u16)src_pixels[1] * 257;
-	out_pixel->b = (u16)src_pixels[0] * 257;
-}
-
-static void XRGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
-{
-	out_pixel->a = (u16)0xffff;
-	out_pixel->r = (u16)src_pixels[2] * 257;
-	out_pixel->g = (u16)src_pixels[1] * 257;
-	out_pixel->b = (u16)src_pixels[0] * 257;
+	out_pixel->a = (u16)a * 257;
+	out_pixel->r = (u16)r * 257;
+	out_pixel->g = (u16)g * 257;
+	out_pixel->b = (u16)b * 257;
 }
 
-static void ARGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
+static void ARGB16161616_to_argb_u16(struct pixel_argb_u16 *out_pixel, int a, int r, int g, int b)
 {
-	u16 *pixels = (u16 *)src_pixels;
-
-	out_pixel->a = le16_to_cpu(pixels[3]);
-	out_pixel->r = le16_to_cpu(pixels[2]);
-	out_pixel->g = le16_to_cpu(pixels[1]);
-	out_pixel->b = le16_to_cpu(pixels[0]);
-}
-
-static void XRGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
-{
-	u16 *pixels = (u16 *)src_pixels;
-
-	out_pixel->a = (u16)0xffff;
-	out_pixel->r = le16_to_cpu(pixels[2]);
-	out_pixel->g = le16_to_cpu(pixels[1]);
-	out_pixel->b = le16_to_cpu(pixels[0]);
+	out_pixel->a = le16_to_cpu(a);
+	out_pixel->r = le16_to_cpu(r);
+	out_pixel->g = le16_to_cpu(g);
+	out_pixel->b = le16_to_cpu(b);
 }
 
-static void RGB565_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
+static void RGB565_to_argb_u16(struct pixel_argb_u16 *out_pixel, const u16 *pixel)
 {
-	u16 *pixels = (u16 *)src_pixels;
-
 	s64 fp_rb_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(31));
 	s64 fp_g_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(63));
 
-	u16 rgb_565 = le16_to_cpu(*pixels);
+	u16 rgb_565 = le16_to_cpu(*pixel);
 	s64 fp_r = drm_int2fixp((rgb_565 >> 11) & 0x1f);
 	s64 fp_g = drm_int2fixp((rgb_565 >> 5) & 0x3f);
 	s64 fp_b = drm_int2fixp(rgb_565 & 0x1f);
@@ -132,34 +130,105 @@ static void RGB565_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
 	out_pixel->b = drm_fixp2int_round(drm_fixp_mul(fp_b, fp_rb_ratio));
 }
 
-/**
- * vkms_compose_row - compose a single row of a plane
- * @stage_buffer: output line with the composed pixels
- * @plane: state of the plane that is being composed
- * @y: y coordinate of the row
+/*
+ * The following functions are read_line function for each pixel format supported by VKMS.
  *
- * This function composes a single row of a plane. It gets the source pixels
- * through the y coordinate (see get_packed_src_addr()) and goes linearly
- * through the source pixel, reading the pixels and converting it to
- * ARGB16161616 (see the pixel_read() callback). For rotate-90 and rotate-270,
- * the source pixels are not traversed linearly. The source pixels are queried
- * on each iteration in order to traverse the pixels vertically.
+ * They read a line starting at the point @x_start,@y_start following the @direction. The result
+ * is stored in @out_pixel and in the format ARGB16161616.
+ *
+ * Those function are very similar, but it is required for performance reason. In the past, some
+ * experiment were done, and with a generic loop the performance are very reduced [1].
+ *
+ * [1]: https://lore.kernel.org/dri-devel/d258c8dc-78e9-4509-9037-a98f7f33b3a3@riseup.net/
  */
-void vkms_compose_row(struct line_buffer *stage_buffer, struct vkms_plane_state *plane, int y)
+
+static void ARGB8888_read_line(struct vkms_frame_info *frame_info, int x_start, int y_start,
+			       enum pixel_read_direction direction, int count,
+			       struct pixel_argb_u16 out_pixel[])
+{
+	u8 *src_pixels = packed_pixels_addr(frame_info, x_start, y_start, 0);
+
+	int step = get_step_1x1(frame_info->fb, direction, 0);
+
+	while (count) {
+		u8 *px = (u8 *)src_pixels;
+
+		ARGB8888_to_argb_u16(out_pixel, px[3], px[2], px[1], px[0]);
+		out_pixel += 1;
+		src_pixels += step;
+		count--;
+	}
+}
+
+static void XRGB8888_read_line(struct vkms_frame_info *frame_info, int x_start, int y_start,
+			       enum pixel_read_direction direction, int count,
+			       struct pixel_argb_u16 out_pixel[])
+{
+	u8 *src_pixels = packed_pixels_addr(frame_info, x_start, y_start, 0);
+
+	int step = get_step_1x1(frame_info->fb, direction, 0);
+
+	while (count) {
+		u8 *px = (u8 *)src_pixels;
+
+		ARGB8888_to_argb_u16(out_pixel, 255, px[2], px[1], px[0]);
+		out_pixel += 1;
+		src_pixels += step;
+		count--;
+	}
+}
+
+static void ARGB16161616_read_line(struct vkms_frame_info *frame_info, int x_start, int y_start,
+				   enum pixel_read_direction direction, int count,
+				   struct pixel_argb_u16 out_pixel[])
+{
+	u8 *src_pixels = packed_pixels_addr(frame_info, x_start, y_start, 0);
+
+	int step = get_step_1x1(frame_info->fb, direction, 0);
+
+	while (count) {
+		u16 *px = (u16 *)src_pixels;
+
+		ARGB16161616_to_argb_u16(out_pixel, px[3], px[2], px[1], px[0]);
+		out_pixel += 1;
+		src_pixels += step;
+		count--;
+	}
+}
+
+static void XRGB16161616_read_line(struct vkms_frame_info *frame_info, int x_start, int y_start,
+				   enum pixel_read_direction direction, int count,
+				   struct pixel_argb_u16 out_pixel[])
+{
+	u8 *src_pixels = packed_pixels_addr(frame_info, x_start, y_start, 0);
+
+	int step = get_step_1x1(frame_info->fb, direction, 0);
+
+	while (count) {
+		u16 *px = (u16 *)src_pixels;
+
+		ARGB16161616_to_argb_u16(out_pixel, 0xFFFF, px[2], px[1], px[0]);
+		out_pixel += 1;
+		src_pixels += step;
+		count--;
+	}
+}
+
+static void RGB565_read_line(struct vkms_frame_info *frame_info, int x_start, int y_start,
+			     enum pixel_read_direction direction, int count,
+			     struct pixel_argb_u16 out_pixel[])
 {
-	struct pixel_argb_u16 *out_pixels = stage_buffer->pixels;
-	struct vkms_frame_info *frame_info = plane->frame_info;
-	u8 *src_pixels = get_packed_src_addr(frame_info, y);
-	int limit = min_t(size_t, drm_rect_width(&frame_info->dst), stage_buffer->n_pixels);
+	u8 *src_pixels = packed_pixels_addr(frame_info, x_start, y_start, 0);
 
-	for (size_t x = 0; x < limit; x++, src_pixels += frame_info->fb->format->cpp[0]) {
-		int x_pos = get_x_position(frame_info, limit, x);
+	int step = get_step_1x1(frame_info->fb, direction, 0);
 
-		if (drm_rotation_90_or_270(frame_info->rotation))
-			src_pixels = get_packed_src_addr(frame_info, x + frame_info->rotated.y1)
-				+ frame_info->fb->format->cpp[0] * y;
+	while (count) {
+		u16 *px = (u16 *)src_pixels;
 
-		plane->pixel_read(src_pixels, &out_pixels[x_pos]);
+		RGB565_to_argb_u16(out_pixel, px);
+		out_pixel += 1;
+		src_pixels += step;
+		count--;
 	}
 }
 
@@ -247,7 +316,7 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
 {
 	struct vkms_frame_info *frame_info = &wb->wb_frame_info;
 	int x_dst = frame_info->dst.x1;
-	u8 *dst_pixels = packed_pixels_addr(frame_info, x_dst, y);
+	u8 *dst_pixels = packed_pixels_addr(frame_info, x_dst, y, 0);
 	struct pixel_argb_u16 *in_pixels = src_buffer->pixels;
 	int x_limit = min_t(size_t, drm_rect_width(&frame_info->dst), src_buffer->n_pixels);
 
@@ -256,27 +325,27 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
 }
 
 /**
- * Retrieve the correct read_pixel function for a specific format.
+ * Retrieve the correct read_line function for a specific format.
  * The returned pointer is NULL for unsupported pixel formats. The caller must ensure that the
  * pointer is valid before using it in a vkms_plane_state.
  *
  * @format: 4cc of the format
  */
-pixel_read_t get_pixel_read_function(u32 format)
+pixel_read_line_t get_pixel_read_line_function(u32 format)
 {
 	switch (format) {
 	case DRM_FORMAT_ARGB8888:
-		return &ARGB8888_to_argb_u16;
+		return &ARGB8888_read_line;
 	case DRM_FORMAT_XRGB8888:
-		return &XRGB8888_to_argb_u16;
+		return &XRGB8888_read_line;
 	case DRM_FORMAT_ARGB16161616:
-		return &ARGB16161616_to_argb_u16;
+		return &ARGB16161616_read_line;
 	case DRM_FORMAT_XRGB16161616:
-		return &XRGB16161616_to_argb_u16;
+		return &XRGB16161616_read_line;
 	case DRM_FORMAT_RGB565:
-		return &RGB565_to_argb_u16;
+		return &RGB565_read_line;
 	default:
-		return (pixel_read_t)NULL;
+		return (pixel_read_line_t)NULL;
 	}
 }
 
diff --git a/drivers/gpu/drm/vkms/vkms_formats.h b/drivers/gpu/drm/vkms/vkms_formats.h
index 3ecea4563254..8d2bef95ff79 100644
--- a/drivers/gpu/drm/vkms/vkms_formats.h
+++ b/drivers/gpu/drm/vkms/vkms_formats.h
@@ -5,7 +5,7 @@
 
 #include "vkms_drv.h"
 
-pixel_read_t get_pixel_read_function(u32 format);
+pixel_read_line_t get_pixel_read_line_function(u32 format);
 
 pixel_write_t get_pixel_write_function(u32 format);
 
diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
index f68b1b03d632..58c1c74742b5 100644
--- a/drivers/gpu/drm/vkms/vkms_plane.c
+++ b/drivers/gpu/drm/vkms/vkms_plane.c
@@ -106,9 +106,9 @@ static void vkms_plane_atomic_update(struct drm_plane *plane,
 		return;
 
 	fmt = fb->format->format;
-	pixel_read_t pixel_read = get_pixel_read_function(fmt);
+	pixel_read_line_t pixel_read_line = get_pixel_read_line_function(fmt);
 
-	if (!pixel_read) {
+	if (!pixel_read_line) {
 		DRM_WARN("Pixel format is not supported by VKMS planes. State is inchanged\n");
 		return;
 	}
@@ -128,10 +128,8 @@ static void vkms_plane_atomic_update(struct drm_plane *plane,
 									  DRM_MODE_REFLECT_X |
 									  DRM_MODE_REFLECT_Y);
 
-	drm_rect_rotate(&frame_info->rotated, drm_rect_width(&frame_info->rotated),
-			drm_rect_height(&frame_info->rotated), frame_info->rotation);
 
-	vkms_plane_state->pixel_read = pixel_read;
+	vkms_plane_state->pixel_read_line = pixel_read_line;
 }
 
 static int vkms_plane_atomic_check(struct drm_plane *plane,

-- 
2.43.0

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