[v3,3/9] drm/vkms: write/update the documentation for pixel conversion and pixel write functions
Commit Message
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Update of outdated comments for pixel_write functions.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 | 4 +++
drivers/gpu/drm/vkms/vkms_drv.h | 13 ++++++++
drivers/gpu/drm/vkms/vkms_formats.c | 58 ++++++++++++++++++++++++++++++------
3 files changed, 66 insertions(+), 9 deletions(-)
Comments
On 26/02/24 05:46, 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 Update of outdated comments for pixel_write functions.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 | 4 +++
> drivers/gpu/drm/vkms/vkms_drv.h | 13 ++++++++
> drivers/gpu/drm/vkms/vkms_formats.c | 58 ++++++++++++++++++++++++++++++------
> 3 files changed, 66 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index c6d9b4a65809..5b341222d239 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -189,6 +189,10 @@ 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. It is a necessary complexity to avoid poor
> + * blending performance.
At this moment in the series, you have not yet reintroduced the
line-by-line algorithm yet. Maybe it's better to add this comment when
you do.
Also, I think it's good to give more context, like:
"The planes are composed line-by-line, instead of pixel-by-pixel"
Best Regards,
~Arthur Grillo
> + */
> 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
> * @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..cb7a49b7c8e7 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.c
> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> @@ -9,6 +9,17 @@
>
> #include "vkms_formats.h"
>
> +/**
> + * packed_pixels_offset() - Get the offset of the block containing 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 be aware that this offset is not always a pointer to a pixel. If individual
> + * pixel values are needed, they have to be extracted from the resulting block.
> + */
> static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int y)
> {
> struct drm_framebuffer *fb = frame_info->fb;
> @@ -17,12 +28,13 @@ 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
> *
> * Takes the information stored in the frame_info, a pair of coordinates, and
> * returns the address of the first color channel.
> @@ -53,6 +65,13 @@ 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)
> {
> /*
> @@ -145,12 +164,11 @@ 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
> + * 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
> + * the writeback buffer.
> */
> static void argb_u16_to_ARGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
> {
> @@ -216,6 +234,14 @@ 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 +255,13 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
> wb->pixel_write(dst_pixels, &in_pixels[x]);
> }
>
> +/**
> + * 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: 4cc of the format
> + */
> void *get_pixel_conversion_function(u32 format)
> {
> switch (format) {
> @@ -247,6 +280,13 @@ void *get_pixel_conversion_function(u32 format)
> }
> }
>
> +/**
> + * 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: 4cc of the format
> + */
> void *get_pixel_write_function(u32 format)
> {
> switch (format) {
>
Le 26/02/24 - 10:07, Arthur Grillo a écrit :
>
>
> On 26/02/24 05:46, 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 | 4 +++
> > drivers/gpu/drm/vkms/vkms_drv.h | 13 ++++++++
> > drivers/gpu/drm/vkms/vkms_formats.c | 58 ++++++++++++++++++++++++++++++------
> > 3 files changed, 66 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> > index c6d9b4a65809..5b341222d239 100644
> > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > @@ -189,6 +189,10 @@ 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. It is a necessary complexity to avoid poor
> > + * blending performance.
>
> At this moment in the series, you have not yet reintroduced the
> line-by-line algorithm yet. Maybe it's better to add this comment when
> you do.
Is it better with this:
/*
* 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.
*/
> Also, I think it's good to give more context, like:
> "The planes are composed line-by-line, instead of pixel-by-pixel"
And after PATCHv3 5/9:
/*
* The planes are composed line-by-line to avoid heavy memory usage. It is a necessary
* complexity to avoid poor blending performance.
*
* The function pixel_read_line callback is used to read a line, using an efficient
* algorithm for a specific format, into the staging buffer.
*/
Kind regards,
Louis Chauvet
> Best Regards,
> ~Arthur Grillo
[...]
On 27/02/24 12:02, Louis Chauvet wrote:
> Le 26/02/24 - 10:07, Arthur Grillo a écrit :
>>
>>
>> On 26/02/24 05:46, 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 | 4 +++
>>> drivers/gpu/drm/vkms/vkms_drv.h | 13 ++++++++
>>> drivers/gpu/drm/vkms/vkms_formats.c | 58 ++++++++++++++++++++++++++++++------
>>> 3 files changed, 66 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
>>> index c6d9b4a65809..5b341222d239 100644
>>> --- a/drivers/gpu/drm/vkms/vkms_composer.c
>>> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
>>> @@ -189,6 +189,10 @@ 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. It is a necessary complexity to avoid poor
>>> + * blending performance.
>>
>> At this moment in the series, you have not yet reintroduced the
>> line-by-line algorithm yet. Maybe it's better to add this comment when
>> you do.
>
> Is it better with this:
>
> /*
> * 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.
> */
>
>> Also, I think it's good to give more context, like:
>> "The planes are composed line-by-line, instead of pixel-by-pixel"
>
> And after PATCHv3 5/9:
>
> /*
> * The planes are composed line-by-line to avoid heavy memory usage. It is a necessary
> * complexity to avoid poor blending performance.
> *
> * The function pixel_read_line callback is used to read a line, using an efficient
> * algorithm for a specific format, into the staging buffer.
> */
>
Hi,
This looks good to me.
Best Regards,
~Arthur Grillo
> Kind regards,
> Louis Chauvet
>
>> Best Regards,
>> ~Arthur Grillo
>
> [...]
>
On Tue, 27 Feb 2024 15:47:08 -0300
Arthur Grillo <arthurgrillo@riseup.net> wrote:
> On 27/02/24 12:02, Louis Chauvet wrote:
> > Le 26/02/24 - 10:07, Arthur Grillo a écrit :
> >>
> >>
> >> On 26/02/24 05:46, 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 | 4 +++
> >>> drivers/gpu/drm/vkms/vkms_drv.h | 13 ++++++++
> >>> drivers/gpu/drm/vkms/vkms_formats.c | 58 ++++++++++++++++++++++++++++++------
> >>> 3 files changed, 66 insertions(+), 9 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> >>> index c6d9b4a65809..5b341222d239 100644
> >>> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> >>> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> >>> @@ -189,6 +189,10 @@ 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. It is a necessary complexity to avoid poor
> >>> + * blending performance.
> >>
> >> At this moment in the series, you have not yet reintroduced the
> >> line-by-line algorithm yet. Maybe it's better to add this comment when
> >> you do.
> >
> > Is it better with this:
> >
> > /*
> > * 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.
> > */
> >
> >> Also, I think it's good to give more context, like:
> >> "The planes are composed line-by-line, instead of pixel-by-pixel"
> >
> > And after PATCHv3 5/9:
> >
> > /*
> > * The planes are composed line-by-line to avoid heavy memory usage. It is a necessary
> > * complexity to avoid poor blending performance.
> > *
> > * The function pixel_read_line callback is used to read a line, using an efficient
> > * algorithm for a specific format, into the staging buffer.
> > */
> >
Hi,
there are a few reasons for the line-by-line algorithm, and the
optimizations at large:
VKMS uses temporary stage and output buffers so that blending functions
can operate on just one high-precision pixel format, struct
pixel_argb_u16. We can make pixel-format-specific read and write
functions completely orthogonal from the blending operations and FB
format combinations. This avoids a combinatorial explosion of needed
functions for { input pixel formats × blending operations × output pixel
formats }.
We can use a temporary stage and output buffer whose size is one line
and not whole FB or CRTC framebuffer. This is the memory savings.
Using a temporary output buffer also avoids repeated
read-decode-blend-encode-write cycles into the final destination
buffer, as we don't need to decode/encode the pixel format.
Finally, doing elementary operations (read, blend, write) line-by-line
is much more efficient than pixel-by-pixel, because it allows making
the inner-most loop very tight. It avoids repeatedly computing a result
that does not change, like which function to call for a specific pixel
format or blending equation.
Thanks,
pq
@@ -189,6 +189,10 @@ 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. It is a necessary complexity to avoid poor
+ * blending performance.
+ */
for (size_t y = 0; y < crtc_y_limit; y++) {
fill_background(&background_color, output_buffer);
@@ -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
* @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;
@@ -9,6 +9,17 @@
#include "vkms_formats.h"
+/**
+ * packed_pixels_offset() - Get the offset of the block containing 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 be aware that this offset is not always a pointer to a pixel. If individual
+ * pixel values are needed, they have to be extracted from the resulting block.
+ */
static size_t pixel_offset(const struct vkms_frame_info *frame_info, int x, int y)
{
struct drm_framebuffer *fb = frame_info->fb;
@@ -17,12 +28,13 @@ 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
*
* Takes the information stored in the frame_info, a pair of coordinates, and
* returns the address of the first color channel.
@@ -53,6 +65,13 @@ 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)
{
/*
@@ -145,12 +164,11 @@ 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
+ * 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
+ * the writeback buffer.
*/
static void argb_u16_to_ARGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
{
@@ -216,6 +234,14 @@ 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 +255,13 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
wb->pixel_write(dst_pixels, &in_pixels[x]);
}
+/**
+ * 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: 4cc of the format
+ */
void *get_pixel_conversion_function(u32 format)
{
switch (format) {
@@ -247,6 +280,13 @@ void *get_pixel_conversion_function(u32 format)
}
}
+/**
+ * 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: 4cc of the format
+ */
void *get_pixel_write_function(u32 format)
{
switch (format) {