Re: [PATCH v8 03/17] drm/vkms: write/update the documentation for pixel conversion and pixel write functions

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On 5/16/24 10:04, Louis Chauvet wrote:
Add some documentation on pixel conversion functions.
Update of outdated comments for pixel_write functions.

Signed-off-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
Acked-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
---
  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

Nit: I know it's not kerneldoc, but I'd be glad if you use
vkms_compose_row()

+	 * 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..212f4ab6a71f 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

s/structure/Structure

+ *
+ * @fb: backing drm framebuffer
+ * @src: source rectangle of this frame in the source framebuffer, stored in 16.16 fixed-point form
+ * @dst: destination rectangle in the crtc buffer, stored in whole pixel units
+ * @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

s/vkms_plane_state/struct vkms_plane_state

+ * ensure that this pointer is valid

Note: "If the @argument description has multiple lines, the continuation
of the description should start at the same column as the previous
line:" [1]

[1] https://docs.kernel.org/doc-guide/kernel-doc.html#function-parameters

   */
  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.

I believe it is @out_pixel.

The content seems great to me, only those minor nits.

Best Regards,
- Maíra

+ *
+ * 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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