Re: [PATCH v5 10/16] drm/vkms: Re-introduce line-per-line composition algorithm

[Maíra Canal <mcanal@xxxxxxxxxx>]

On 3/13/24 14:45, 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 focused 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 maintainability 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 remaining complexity is around the clipping, to
> avoid reading/writing outside 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 for color
> conversion were introduced to avoid code repetition:
> - *_to_argb_u16: 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)
> - kms_rotation (for all rotations and formats combinations) [3]
> The performance gain was mesured with:
> - kms_fb_stress

Could you tell us what was the performance gain?

> [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/
> [3]:
>
> Signed-off-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
> ---
>   drivers/gpu/drm/vkms/vkms_composer.c | 167 +++++++++++++++++++------
>   drivers/gpu/drm/vkms/vkms_drv.h      |  27 ++--
>   drivers/gpu/drm/vkms/vkms_formats.c  | 236 ++++++++++++++++++++++-------------
>   drivers/gpu/drm/vkms/vkms_formats.h  |   2 +-
>   drivers/gpu/drm/vkms/vkms_plane.c    |   5 +-
>   5 files changed, 292 insertions(+), 145 deletions(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index 989bcf59f375..5d78c33dbf41 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -41,7 +41,7 @@ static void pre_mul_alpha_blend(const struct line_buffer *stage_buffer,
>   				struct line_buffer *output_buffer, int x_start, int pixel_count)
>   {
>   	struct pixel_argb_u16 *out = &output_buffer->pixels[x_start];
> -	const struct pixel_argb_u16 *in = stage_buffer->pixels;
> +	const struct pixel_argb_u16 *in = &stage_buffer->pixels[x_start];
>   
>   	for (int i = 0; i < pixel_count; i++) {
>   		out[i].a = (u16)0xffff;
> @@ -51,33 +51,6 @@ static void pre_mul_alpha_blend(const struct line_buffer *stage_buffer,
>   	}
>   }
>   
> -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)
> @@ -215,34 +188,146 @@ 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, x_dst, x_limit;
>   
>   	const struct pixel_argb_u16 background_color = { .a = 0xffff };
>   
> -	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
> +	int crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
> +	int crtc_x_limit = crtc_state->base.crtc->mode.hdisplay;

Shouldn't it be `unsigned int`?

>   
>   	/*
>   	 * The planes are composed line-by-line to avoid heavy memory usage. It is a necessary
>   	 * complexity to avoid poor blending performance.
>   	 *
> -	 * The function vkms_compose_row is used to read a line, pixel-by-pixel, into the staging
> -	 * buffer.
> +	 * The function pixel_read_line callback is used to read a line, using an efficient
> +	 * algorithm for a specific format, into the staging buffer.
>   	 */
>   	for (size_t y = 0; y < crtc_y_limit; y++) {
>   		fill_background(&background_color, output_buffer);
>   
>   		/* The active planes are composed associatively in z-order. */
>   		for (size_t i = 0; i < n_active_planes; i++) {
> -			x_dst = plane[i]->frame_info->dst.x1;
> -			x_limit = min_t(size_t, drm_rect_width(&plane[i]->frame_info->dst),
> -					stage_buffer->n_pixels);
> -			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(stage_buffer, output_buffer, x_dst, x_limit);
> +			/*
> +			 * dst_line 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 dst_line = DRM_RECT_INIT(

Please, run checkpatch on this patch.

> +				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_line to the crtc_x_limit to avoid writing outside of
> +			 * the destination buffer
> +			 */
> +			dst_line.x1 = max_t(int, dst_line.x1, 0);
> +			dst_line.x2 = min_t(int, dst_line.x2, crtc_x_limit);
> +			/* The destination is completely outside of the crtc. */
> +			if (dst_line.x2 <= dst_line.x1)
> +				continue;
> +
> +			struct drm_rect src_line = dst_line;
> +
> +			/*
> +			 * 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_line, -current_plane->frame_info->dst.x1,
> +					   -current_plane->frame_info->dst.y1);
> +			drm_rect_rotate_inv(&src_line,
> +					    drm_rect_width(&tmp_src),
> +					    drm_rect_height(&tmp_src),
> +					    current_plane->frame_info->rotation);
> +			drm_rect_translate(&src_line, 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_line.x1;
> +			int y_start = src_line.y1;
> +			int pixel_count;
> +			/* [2]: Compute and clamp the number of pixel to read */
> +			if (direction == READ_LEFT_TO_RIGHT || direction == READ_RIGHT_TO_LEFT) {
> +				/*
> +				 * In horizontal reading, the src_line width is the number of pixel
> +				 * to read
> +				 */
> +				pixel_count = drm_rect_width(&src_line);
> +				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_line height is the number of pixel
> +				 * to read
> +				 */
> +				pixel_count = drm_rect_height(&src_line);
> +				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_line is the top-left corner, so when reading READ_RIGHT_TO_LEFT or
> +			 * READ_BOTTOM_TO_TOP, it must be changed to the top-right/bottom-left
> +			 * corner.
> +			 */
> +			if (direction == READ_RIGHT_TO_LEFT) {
> +				// x_start is now the right point
> +				x_start += pixel_count - 1;
> +			} else if (direction == READ_BOTTOM_TO_TOP) {
> +				// y_start is now the bottom point
> +				y_start += pixel_count - 1;
> +			}

Any chance this code could be a separate function? I believe it would
make it more readable.

Best Regards,
- Maíra

> +
> +			/*
> +			 * 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, 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);
> @@ -250,7 +335,7 @@ static void blend(struct vkms_writeback_job *wb,
>   		*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);
>   	}
>   }
>   
> @@ -261,7 +346,7 @@ 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 985e7a92b7bc..23e1d247468d 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;
>   };
> @@ -80,26 +79,37 @@ enum pixel_read_direction {
>   	READ_LEFT_TO_RIGHT
>   };
>   
> +struct vkms_plane_state;
> +
>   /**
> - * typedef pixel_read_t - These functions are used to read a pixel in the source frame,
> + * 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.
>    *
> - * @in_pixel: Pointer to the pixel to read
> - * @out_pixel: Pointer to write the converted pixel
> + * @plane: Plane used as source for the pixel value
> + * @x_start: X (width) coordinate of the first pixel to copy. The caller must ensure that x_start
> + * is positive and smaller than @plane->frame_info->fb->width.
> + * @y_start: Y (width) coordinate of the first pixel to copy. The caller must ensure that y_start
> + * is positive and smaller than @plane->frame_info->fb->height.
> + * @direction: Direction to use for the copy, starting at @x_start/@y_start
> + * @count: Number of pixels to copy
> + * @out_pixel: Pointer where to write the pixel values. They will be written from @out_pixel[0]
> + * to @out_pixel[@count]. The caller must ensure that out_pixel have a length of at least @count.
>    */
> -typedef void (*pixel_read_t)(const u8 *in_pixel, struct pixel_argb_u16 *out_pixel);
> +typedef void (*pixel_read_line_t)(const struct vkms_plane_state *plane, 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
>    * @base: base plane state
>    * @frame_info: data required for composing computation
> - * @pixel_read: function to read a pixel in this plane. The creator of a vkms_plane_state must
> - * ensure that this pointer is valid
> + * @pixel_read_line: function to read a pixel line in this plane. The creator of a vkms_plane_state
> + * must ensure that this pointer is valid
>    */
>   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 {
> @@ -204,7 +214,6 @@ 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 743b6fd06db5..1449a0e6c706 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.c
> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> @@ -105,77 +105,45 @@ static int get_step_next_block(struct drm_framebuffer *fb, enum pixel_read_direc
>   	return 0;
>   }
>   
> -static void *get_packed_src_addr(const struct vkms_frame_info *frame_info, int y,
> -				 int plane_index)
> -{
> -	int x_src = frame_info->src.x1 >> 16;
> -	int y_src = y - frame_info->rotated.y1 + (frame_info->src.y1 >> 16);
> -	u8 *addr;
> -	int rem_x, rem_y;
> -
> -	packed_pixels_addr(frame_info, x_src, y_src, plane_index, &addr, &rem_x, &rem_y);
> -	return addr;
> -}
> -
> -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(const u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
> +static struct pixel_argb_u16 argb_u16_from_u8888(int a, int r, int g, int b)
>   {
> +	struct pixel_argb_u16 out_pixel;
>   	/*
>   	 * The 257 is the "conversion ratio". This number is obtained by the
>   	 * (2^16 - 1) / (2^8 - 1) division. Which, in this case, tries to get
>   	 * the best color value in a pixel format with more possibilities.
>   	 * A similar idea applies to others RGB color conversions.
>   	 */
> -	out_pixel->a = (u16)in_pixel[3] * 257;
> -	out_pixel->r = (u16)in_pixel[2] * 257;
> -	out_pixel->g = (u16)in_pixel[1] * 257;
> -	out_pixel->b = (u16)in_pixel[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 XRGB8888_to_argb_u16(const u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
> -{
> -	out_pixel->a = (u16)0xffff;
> -	out_pixel->r = (u16)in_pixel[2] * 257;
> -	out_pixel->g = (u16)in_pixel[1] * 257;
> -	out_pixel->b = (u16)in_pixel[0] * 257;
> +	return out_pixel;
>   }
>   
> -static void ARGB16161616_to_argb_u16(const u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
> +static struct pixel_argb_u16 argb_u16_from_u16161616(int a, int r, int g, int b)
>   {
> -	u16 *pixel = (u16 *)in_pixel;
> +	struct pixel_argb_u16 out_pixel;
>   
> -	out_pixel->a = le16_to_cpu(pixel[3]);
> -	out_pixel->r = le16_to_cpu(pixel[2]);
> -	out_pixel->g = le16_to_cpu(pixel[1]);
> -	out_pixel->b = le16_to_cpu(pixel[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 XRGB16161616_to_argb_u16(const u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
> -{
> -	u16 *pixel = (u16 *)in_pixel;
> -
> -	out_pixel->a = (u16)0xffff;
> -	out_pixel->r = le16_to_cpu(pixel[2]);
> -	out_pixel->g = le16_to_cpu(pixel[1]);
> -	out_pixel->b = le16_to_cpu(pixel[0]);
> +	return out_pixel;
>   }
>   
> -static void RGB565_to_argb_u16(const u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
> +static struct pixel_argb_u16 argb_u16_from_RGB565(const u16 *pixel)
>   {
> -	u16 *pixel = (u16 *)in_pixel;
> +	struct pixel_argb_u16 out_pixel;
>   
>   	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));
> @@ -185,12 +153,26 @@ static void RGB565_to_argb_u16(const u8 *in_pixel, struct pixel_argb_u16 *out_pi
>   	s64 fp_g = drm_int2fixp((rgb_565 >> 5) & 0x3f);
>   	s64 fp_b = drm_int2fixp(rgb_565 & 0x1f);
>   
> -	out_pixel->a = (u16)0xffff;
> -	out_pixel->r = drm_fixp2int_round(drm_fixp_mul(fp_r, fp_rb_ratio));
> -	out_pixel->g = drm_fixp2int_round(drm_fixp_mul(fp_g, fp_g_ratio));
> -	out_pixel->b = drm_fixp2int_round(drm_fixp_mul(fp_b, fp_rb_ratio));
> +	out_pixel.a = (u16)0xffff;
> +	out_pixel.r = drm_fixp2int_round(drm_fixp_mul(fp_r, fp_rb_ratio));
> +	out_pixel.g = drm_fixp2int_round(drm_fixp_mul(fp_g, fp_g_ratio));
> +	out_pixel.b = drm_fixp2int_round(drm_fixp_mul(fp_b, fp_rb_ratio));
> +
> +	return out_pixel;
>   }
>   
> +/*
> + * The following functions are read_line function for each pixel format supported by VKMS.
> + *
> + * 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/
> + */
> +
>   /**
>    * black_to_argb_u16() - pixel_read callback which always read black
>    *
> @@ -198,42 +180,116 @@ static void RGB565_to_argb_u16(const u8 *in_pixel, struct pixel_argb_u16 *out_pi
>    * It is used to avoid null pointer to be used as a function. In theory, this function should
>    * never be called, except if you found a bug in the driver/DRM core.
>    */
> -static void black_to_argb_u16(const u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
> +static void black_to_argb_u16(const struct vkms_plane_state *plane, int x_start,
> +			      int y_start, enum pixel_read_direction direction, int count,
> +			      struct pixel_argb_u16 out_pixel[])
>   {
> -	out_pixel->a = (u16)0xFFFF;
> -	out_pixel->r = 0;
> -	out_pixel->g = 0;
> -	out_pixel->b = 0;
> +	struct pixel_argb_u16 *end = out_pixel + count;
> +
> +	while (out_pixel < end) {
> +		*out_pixel = argb_u16_from_u8888(255, 0, 0, 0);
> +		out_pixel += 1;
> +	}
>   }
>   
> -/**
> - * 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
> - *
> - * 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.
> - */
> -void vkms_compose_row(struct line_buffer *stage_buffer, struct vkms_plane_state *plane, int y)
> +static void ARGB8888_read_line(const struct vkms_plane_state *plane, 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, 0);
> -	int limit = min_t(size_t, drm_rect_width(&frame_info->dst), stage_buffer->n_pixels);
> +	struct pixel_argb_u16 *end = out_pixel + count;
> +	u8 *src_pixels;
> +	int rem_x, rem_y;
> +
> +	packed_pixels_addr(plane->frame_info, x_start, y_start, 0, &src_pixels, &rem_x, &rem_y);
> +
> +	int step = get_step_next_block(plane->frame_info->fb, direction, 0);
> +
> +	while (out_pixel < end) {
> +		u8 *px = (u8 *)src_pixels;
> +		*out_pixel = argb_u16_from_u8888(px[3], px[2], px[1], px[0]);
> +		out_pixel += 1;
> +		src_pixels += step;
> +	}
> +}
> +
> +static void XRGB8888_read_line(const struct vkms_plane_state *plane, int x_start, int y_start,
> +			       enum pixel_read_direction direction, int count,
> +			       struct pixel_argb_u16 out_pixel[])
> +{
> +	struct pixel_argb_u16 *end = out_pixel + count;
> +	u8 *src_pixels;
> +	int rem_x, rem_y;
> +
> +	packed_pixels_addr(plane->frame_info, x_start, y_start, 0, &src_pixels, &rem_x, &rem_y);
> +
> +	int step = get_step_next_block(plane->frame_info->fb, direction, 0);
> +
> +	while (out_pixel < end) {
> +		u8 *px = (u8 *)src_pixels;
> +		*out_pixel = argb_u16_from_u8888(255, px[2], px[1], px[0]);
> +		out_pixel += 1;
> +		src_pixels += step;
> +	}
> +}
> +
> +static void ARGB16161616_read_line(const struct vkms_plane_state *plane, int x_start,
> +				   int y_start, enum pixel_read_direction direction, int count,
> +				   struct pixel_argb_u16 out_pixel[])
> +{
> +	struct pixel_argb_u16 *end = out_pixel + count;
> +	u8 *src_pixels;
> +	int rem_x, rem_y;
> +
> +	packed_pixels_addr(plane->frame_info, x_start, y_start, 0, &src_pixels, &rem_x, &rem_y);
> +
> +	int step = get_step_next_block(plane->frame_info->fb, direction, 0);
> +
> +	while (out_pixel < end) {
> +		u16 *px = (u16 *)src_pixels;
> +		*out_pixel = argb_u16_from_u16161616(px[3], px[2], px[1], px[0]);
> +		out_pixel += 1;
> +		src_pixels += step;
> +	}
> +}
> +
> +static void XRGB16161616_read_line(const struct vkms_plane_state *plane, int x_start,
> +				   int y_start, enum pixel_read_direction direction, int count,
> +				   struct pixel_argb_u16 out_pixel[])
> +{
> +	struct pixel_argb_u16 *end = out_pixel + count;
> +	u8 *src_pixels;
> +	int rem_x, rem_y;
> +
> +	packed_pixels_addr(plane->frame_info, x_start, y_start, 0, &src_pixels, &rem_x, &rem_y);
> +
> +	int step = get_step_next_block(plane->frame_info->fb, direction, 0);
> +
> +	while (out_pixel < end) {
> +		u16 *px = (u16 *)src_pixels;
> +		*out_pixel = argb_u16_from_u16161616(0xFFFF, px[2], px[1], px[0]);
> +		out_pixel += 1;
> +		src_pixels += step;
> +	}
> +}
> +
> +static void RGB565_read_line(const struct vkms_plane_state *plane, int x_start,
> +			     int y_start, enum pixel_read_direction direction, int count,
> +			     struct pixel_argb_u16 out_pixel[])
> +{
> +	struct pixel_argb_u16 *end = out_pixel + count;
> +	u8 *src_pixels;
> +	int rem_x, rem_y;
> +
> +	packed_pixels_addr(plane->frame_info, x_start, y_start, 0, &src_pixels, &rem_x, &rem_y);
>   
> -	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_next_block(plane->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, 0)
> -				+ frame_info->fb->format->cpp[0] * y;
> +	while (out_pixel < end) {
> +		u16 *px = (u16 *)src_pixels;
>   
> -		plane->pixel_read(src_pixels, &out_pixels[x_pos]);
> +		*out_pixel = argb_u16_from_RGB565(px);
> +		out_pixel += 1;
> +		src_pixels += step;
>   	}
>   }
>   
> @@ -343,25 +399,25 @@ 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.
>    * If the format is not supported by VKMS a warn is emitted and a dummy "always read black"
>    * function is returned.
>    *
>    * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
>    */
> -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:
>   		/*
>   		 * This is a bug in vkms_plane_atomic_check. All the supported
> 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 10e9b23dab28..8875bed76410 100644
> --- a/drivers/gpu/drm/vkms/vkms_plane.c
> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> @@ -112,7 +112,6 @@ static void vkms_plane_atomic_update(struct drm_plane *plane,
>   	frame_info = vkms_plane_state->frame_info;
>   	memcpy(&frame_info->src, &new_state->src, sizeof(struct drm_rect));
>   	memcpy(&frame_info->dst, &new_state->dst, sizeof(struct drm_rect));
> -	memcpy(&frame_info->rotated, &new_state->dst, sizeof(struct drm_rect));
>   	frame_info->fb = fb;
>   	memcpy(&frame_info->map, &shadow_plane_state->data, sizeof(frame_info->map));
>   	drm_framebuffer_get(frame_info->fb);
> @@ -122,10 +121,8 @@ 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 = get_pixel_read_function(fmt);
> +	vkms_plane_state->pixel_read_line = get_pixel_read_line_function(fmt);
>   }
>   
>   static int vkms_plane_atomic_check(struct drm_plane *plane,