Re: [PATCH v2 5/9] drm/vkms: Re-introduce line-per-line composition algorithm

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Hi Louis,

On 2/23/24 08:37, Louis Chauvet wrote:
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.

s/focussed/focused


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.

s/maintenability/maintainability

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

s/remaning/remaining

avoid reading/writing oudside source/destination buffers.

s/oudside/outside


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@xxxxxxxxx/
[2]: commit 322d716a3e8a ("drm/vkms: isolate pixel conversion
      functionality")
      https://lore.kernel.org/all/20230418130525.128733-2-mcanal@xxxxxxxxxx/

Signed-off-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
---

[...]

+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

This doesn't compile.

Best Regards,
- Maíra

+ * 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@xxxxxxxxxx/
   */
-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,




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