Re: [PATCH v5 03/16] drm/vkms: write/update the documentation for pixel conversion and pixel write functions

[Louis Chauvet <louis.chauvet@bootlin.com>]

Le 25/03/24 - 10:32, Maíra Canal a écrit :
> 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 Update of outdated comments for pixel_write functions.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@bootlin.com>
> > ---
> >   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".

Fixed in v6.
 
> >    * @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.

I just followed what was here before, fixed for the v6.

> >    *
> >    * 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.

Fixed in v6.

> > + * 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

Thanks for this reference, fixed for the v6

> > + */
> > +
> >   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].

Fixed in v6.

> > + * 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.

Fixed in v6.

> > + * 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?

Fixed for the v6.

> > + * 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.

Fixed for the v6.

Thanks,
Louis Chauvet

> 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) {
> > 

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com