Re: [PATCH v5 03/16] drm/vkms: write/update the documentation for pixel conversion and pixel write functions
From: Maíra Canal
Date: Mon Mar 25 2024 - 13:55:53 EST
On 3/13/24 14:44, 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Update of outdated comments for pixel_write functions.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>
---
drivers/gpu/drm/vkms/vkms_composer.c | 7 ++++
drivers/gpu/drm/vkms/vkms_drv.h | 13 ++++++++
drivers/gpu/drm/vkms/vkms_formats.c | 62 ++++++++++++++++++++++++++++++------
3 files changed, 73 insertions(+), 9 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..18086423a3a7 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
+ * @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;
@@ -52,6 +63,8 @@ struct vkms_writeback_job {
* vkms_plane_state - Driver specific plane state
It should be "* 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 172830a3936a..6e3dc8682ff9 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;
@@ -17,18 +29,22 @@ static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int
+ (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
I would add a space after x and y.
*
* 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)
@@ -53,6 +69,13 @@ 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
Double-spacing.
+ * ARGB16161616 in out_pixel.
+ *
+ * They are used in the `vkms_compose_row` function to handle multiple formats.
For cross-referencing functions, we use vkms_compose_row() [1].
[1]
https://docs.kernel.org/doc-guide/kernel-doc.html#highlights-and-cross-references
+ */
+
static void ARGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
{
/*
@@ -145,12 +168,11 @@ 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 argb_u16 pixel and convert it to a specific format. The
For cross-referencing structs, look here [1].
+ * 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 the `vkms_writeback_row` to convert and store a pixel from the src_buffer to
Same.
+ * the writeback buffer.
*/
static void argb_u16_to_ARGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
{
@@ -216,6 +238,14 @@ static void argb_u16_to_RGB565(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
*pixels = cpu_to_le16(r << 11 | g << 5 | b);
}
+/**
+ * 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)
{
@@ -229,6 +259,13 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
wb->pixel_write(dst_pixels, &in_pixels[x]);
}
+/**
Where is the function name?
+ * 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) {
@@ -247,6 +284,13 @@ void *get_pixel_conversion_function(u32 format)
}
}
+/**
Same.
Best Regards,
- Maíra
+ * 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) {