Re: [PATCH v6 03/17] drm/vkms: write/update the documentation for pixel conversion and pixel write functions

[Pekka Paalanen]

On Tue, 09 Apr 2024 15:25:21 +0200
Louis Chauvet <louis.chauvet@xxxxxxxxxxx> wrote:

> Add some documentation on pixel conversion functions.
> Update of outdated comments for pixel_write functions.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
> ---
>  drivers/gpu/drm/vkms/vkms_composer.c |  7 ++++
>  drivers/gpu/drm/vkms/vkms_drv.h      | 15 ++++++++-
>  drivers/gpu/drm/vkms/vkms_formats.c  | 62 ++++++++++++++++++++++++++++++------
>  3 files changed, 74 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index c6d9b4a65809..da0651a94c9b 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -189,6 +189,13 @@ static void blend(struct vkms_writeback_job *wb,
>  
>  	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
>  
> +	/*
> +	 * 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.
> +	 */
>  	for (size_t y = 0; y < crtc_y_limit; y++) {
>  		fill_background(&background_color, output_buffer);
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index b4b357447292..a86cb537d6aa 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -25,6 +25,17 @@
>  
>  #define VKMS_LUT_SIZE 256
>  
> +/**
> + * struct vkms_frame_info - structure to store the state of a frame
> + *
> + * @fb: backing drm framebuffer
> + * @src: source rectangle of this frame in the source framebuffer
> + * @dst: destination rectangle in the crtc buffer

Are both src and dst using whole pixel units, or is src using 1/65536th
pixel units?

Asking because UAPI has src rect in 16.16 fixed-point, IIRC.

With that clarified:

Acked-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>


Thanks,
pq

> + * @map: see drm_shadow_plane_state@data
> + * @rotation: rotation applied to the source.
> + *
> + * @src and @dst should have the same size modulo the rotation.
> + */
>  struct vkms_frame_info {
>  	struct drm_framebuffer *fb;
>  	struct drm_rect src, dst;
> @@ -49,9 +60,11 @@ struct vkms_writeback_job {
>  };
>  
>  /**
> - * vkms_plane_state - Driver specific plane state
> + * struct 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
>   */
>  struct vkms_plane_state {
>  	struct drm_shadow_plane_state base;
> diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> index d597c48452ac..f157c43da4d6 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.c
> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> @@ -9,6 +9,18 @@
>  
>  #include "vkms_formats.h"
>  
> +/**
> + * pixel_offset() - Get the offset of 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
> + *
> + * The caller must ensure that the framebuffer associated with this request uses a pixel format
> + * where block_h == block_w == 1.
> + * If this requirement is not fulfilled, the resulting offset can point to an other pixel or
> + * outside of the buffer.
> + */
>  static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int y)
>  {
>  	struct drm_framebuffer *fb = frame_info->fb;
> @@ -16,18 +28,22 @@ static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int
>  	return fb->offsets[0] + (y * fb->pitches[0]) + (x * fb->format->cpp[0]);
>  }
>  
> -/*
> - * packed_pixels_addr - Get the pointer to pixel of a given pair of coordinates
> +/**
> + * packed_pixels_addr() - Get the pointer to the block containing the pixel at the given
> + * coordinates
>   *
>   * @frame_info: Buffer metadata
> - * @x: The x(width) coordinate of the 2D buffer
> - * @y: The y(Heigth) coordinate of the 2D buffer
> + * @x: The x (width) coordinate inside the plane
> + * @y: The y (height) coordinate inside 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).
> + *
> + * The caller must ensure that the framebuffer associated with this request uses a pixel format
> + * where block_h == block_w == 1, otherwise the returned pointer can be outside the buffer.
>   */
>  static void *packed_pixels_addr(const struct vkms_frame_info *frame_info,
>  				int x, int y)
> @@ -52,6 +68,13 @@ static int get_x_position(const struct vkms_frame_info *frame_info, int limit, i
>  	return x;
>  }
>  
> +/*
> + * The following functions take pixel data from the buffer and convert them to the format
> + * ARGB16161616 in out_pixel.
> + *
> + * They are used in the vkms_compose_row() function to handle multiple formats.
> + */
> +
>  static void ARGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
>  {
>  	/*
> @@ -144,12 +167,11 @@ void vkms_compose_row(struct line_buffer *stage_buffer, struct vkms_plane_state
>  }
>  
>  /*
> - * The following  functions take an line of argb_u16 pixels from the
> - * src_buffer, convert them to a specific format, and store them in the
> - * destination.
> + * The following functions take one &struct pixel_argb_u16 and convert it to a specific format.
> + * The result is stored in @dst_pixels.
>   *
> - * They are used in the `compose_active_planes` to convert and store a line
> - * from the src_buffer to the writeback buffer.
> + * They are used in vkms_writeback_row() to convert and store a pixel from the src_buffer to
> + * the writeback buffer.
>   */
>  static void argb_u16_to_ARGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
>  {
> @@ -215,6 +237,14 @@ static void argb_u16_to_RGB565(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
>  	*pixels = cpu_to_le16(r << 11 | g << 5 | b);
>  }
>  
> +/**
> + * vkms_writeback_row() - Generic loop for all supported writeback format. It is executed just
> + * after the blending to write a line in the writeback buffer.
> + *
> + * @wb: Job where to insert the final image
> + * @src_buffer: Line to write
> + * @y: Row to write in the writeback buffer
> + */
>  void vkms_writeback_row(struct vkms_writeback_job *wb,
>  			const struct line_buffer *src_buffer, int y)
>  {
> @@ -228,6 +258,13 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
>  		wb->pixel_write(dst_pixels, &in_pixels[x]);
>  }
>  
> +/**
> + * get_pixel_conversion_function() - Retrieve the correct read_pixel 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: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
> + */
>  void *get_pixel_conversion_function(u32 format)
>  {
>  	switch (format) {
> @@ -246,6 +283,13 @@ void *get_pixel_conversion_function(u32 format)
>  	}
>  }
>  
> +/**
> + * get_pixel_write_function() - Retrieve the correct write_pixel 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_writeback_job.
> + *
> + * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
> + */
>  void *get_pixel_write_function(u32 format)
>  {
>  	switch (format) {
>

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