Re: [PATCH v11 10/15] drm/vkms: Add YUV support

[Randy Dunlap <rdunlap@infradead.org>]

On 9/30/24 8:31 AM, Louis Chauvet wrote:
> From: Arthur Grillo <arthurgrillo@riseup.net>
> 
> Add support to the YUV formats bellow:
> 
> - NV12/NV16/NV24
> - NV21/NV61/NV42
> - YUV420/YUV422/YUV444
> - YVU420/YVU422/YVU444
> 
> The conversion from yuv to rgb is done with fixed-point arithmetic, using
> 32.32 fixed-point numbers and the drm_fixed helpers.
> 
> To do the conversion, a specific matrix must be used for each color range
> (DRM_COLOR_*_RANGE) and encoding (DRM_COLOR_*). This matrix is stored in
> the `conversion_matrix` struct, along with the specific y_offset needed.
> This matrix is queried only once, in `vkms_plane_atomic_update` and
> stored in a `vkms_plane_state`. Those conversion matrices of each
> encoding and range were obtained by rounding the values of the original
> conversion matrices multiplied by 2^32. This is done to avoid the use of
> floating point operations.
> 
> The same reading function is used for YUV and YVU formats. As the only
> difference between those two category of formats is the order of field, a
> simple swap in conversion matrix columns allows using the same function.
> 
> Signed-off-by: Arthur Grillo <arthurgrillo@riseup.net>
> [Louis Chauvet:
> - Adapted Arthur's work
> - Implemented the read_line_t callbacks for yuv
> - add struct conversion_matrix
> - store the whole conversion_matrix in the plane state
> - remove struct pixel_yuv_u8
> - update the commit message
> - Merge the modifications from Arthur]
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>  drivers/gpu/drm/vkms/vkms_drv.h     |  18 ++
>  drivers/gpu/drm/vkms/vkms_formats.c | 353 ++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/vkms/vkms_formats.h |   4 +
>  drivers/gpu/drm/vkms/vkms_plane.c   |  16 +-
>  4 files changed, 390 insertions(+), 1 deletion(-)
> 

> diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> index 0f6678420a11..adb1228e5201 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.c
> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> @@ -140,6 +140,51 @@ static void packed_pixels_addr_1x1(const struct vkms_frame_info *frame_info,
>  	*addr = (u8 *)frame_info->map[0].vaddr + offset;
>  }
>  
> +/**
> + * get_subsampling() - Get the subsampling divisor value on a specific direction
> + *
> + * @format: format to extarct the subsampling from

                         extract

> + * @direction: direction of the subsampling requested
> + */
> +static int get_subsampling(const struct drm_format_info *format,
> +			   enum pixel_read_direction direction)
> +{
> +	switch (direction) {
> +	case READ_BOTTOM_TO_TOP:
> +	case READ_TOP_TO_BOTTOM:
> +		return format->vsub;
> +	case READ_RIGHT_TO_LEFT:
> +	case READ_LEFT_TO_RIGHT:
> +		return format->hsub;
> +	}
> +	WARN_ONCE(true, "Invalid direction for pixel reading: %d\n", direction);
> +	return 1;
> +}
> +
> +/**
> + * get_subsampling_offset() - An offset for keeping the chroma siting consistent regardless of
> + * x_start and y_start values
> + *
> + * @direction: direction of the reading to properly compute this offset
> + * @x_start: x coordinate of the starting point of the readed line

                                                          read

> + * @y_start: y coordinate of the starting point of the readed line

                                                          read

> + */
> +static int get_subsampling_offset(enum pixel_read_direction direction, int x_start, int y_start)
> +{