Re: [PATCH v5 09/16] drm/vkms: Introduce pixel_read_direction enum

["Maíra Canal" <mcanal@igalia.com>]

On 3/13/24 14:45, Louis Chauvet wrote:
> The pixel_read_direction enum is useful to describe the reading direction
> in a plane. It avoids using the rotation property of DRM, which not
> practical to know the direction of reading.
> This patch also introduce two helpers, one to compute the
> pixel_read_direction from the DRM rotation property, and one to compute
> the step, in byte, between two successive pixel in a specific direction.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>   drivers/gpu/drm/vkms/vkms_composer.c | 36 ++++++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/vkms/vkms_drv.h      | 11 +++++++++++
>   drivers/gpu/drm/vkms/vkms_formats.c  | 30 ++++++++++++++++++++++++++++++
>   3 files changed, 77 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index 9254086f23ff..989bcf59f375 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -159,6 +159,42 @@ static void apply_lut(const struct vkms_crtc_state *crtc_state, struct line_buff
>   	}
>   }
>   
> +/**
> + * direction_for_rotation() - Get the correct reading direction for a given rotation
> + *
> + * This function will use the @rotation setting of a source plane to compute the reading
> + * direction in this plane which correspond to a "left to right writing" in the CRTC.
> + * For example, if the buffer is reflected on X axis, the pixel must be read from right to left
> + * to be written from left to right on the CRTC.
> + *
> + * @rotation: Rotation to analyze. It correspond the field @frame_info.rotation.

A bit unusual to see arguments after the description.

> + */
> +static enum pixel_read_direction direction_for_rotation(unsigned int rotation)
> +{
> +	if (rotation & DRM_MODE_ROTATE_0) {
> +		if (rotation & DRM_MODE_REFLECT_X)
> +			return READ_RIGHT_TO_LEFT;
> +		else
> +			return READ_LEFT_TO_RIGHT;
> +	} else if (rotation & DRM_MODE_ROTATE_90) {
> +		if (rotation & DRM_MODE_REFLECT_Y)
> +			return READ_BOTTOM_TO_TOP;
> +		else
> +			return READ_TOP_TO_BOTTOM;
> +	} else if (rotation & DRM_MODE_ROTATE_180) {
> +		if (rotation & DRM_MODE_REFLECT_X)
> +			return READ_LEFT_TO_RIGHT;
> +		else
> +			return READ_RIGHT_TO_LEFT;
> +	} else if (rotation & DRM_MODE_ROTATE_270) {
> +		if (rotation & DRM_MODE_REFLECT_Y)
> +			return READ_TOP_TO_BOTTOM;
> +		else
> +			return READ_BOTTOM_TO_TOP;
> +	}
> +	return READ_LEFT_TO_RIGHT;
> +}
> +
>   /**
>    * blend - blend the pixels from all planes and compute crc
>    * @wb: The writeback frame buffer metadata
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 3ead8b39af4a..985e7a92b7bc 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -69,6 +69,17 @@ struct vkms_writeback_job {
>   	pixel_write_t pixel_write;
>   };
>   
> +/**
> + * enum pixel_read_direction - Enum used internaly by VKMS to represent a reading direction in a
> + * plane.
> + */
> +enum pixel_read_direction {
> +	READ_BOTTOM_TO_TOP,
> +	READ_TOP_TO_BOTTOM,
> +	READ_RIGHT_TO_LEFT,
> +	READ_LEFT_TO_RIGHT
> +};
> +
>   /**
>    * typedef pixel_read_t - These functions are used to read a pixel in the source frame,
>    * convert it to `struct pixel_argb_u16` and write it to @out_pixel.
> diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> index 649d75d05b1f..743b6fd06db5 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.c
> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> @@ -75,6 +75,36 @@ static void packed_pixels_addr(const struct vkms_frame_info *frame_info,
>   	*addr = (u8 *)frame_info->map[0].vaddr + offset;
>   }
>   
> +/**
> + * get_step_next_block() - Common helper to compute the correct step value between each pixel block
> + * to read in a certain direction.
> + *
> + * As the returned offset is the number of bytes between two consecutive blocks in a direction,
> + * the caller may have to read multiple pixel before using the next one (for example, to read from
> + * left to right in a DRM_FORMAT_R1 plane, each block contains 8 pixels, so the step must be used
> + * only every 8 pixels.
> + *
> + * @fb: Framebuffer to iter on
> + * @direction: Direction of the reading
> + * @plane_index: Plane to get the step from

Same.

Best Regards,
- Maíra

> + */
> +static int get_step_next_block(struct drm_framebuffer *fb, enum pixel_read_direction direction,
> +			       int plane_index)
> +{
> +	switch (direction) {
> +	case READ_LEFT_TO_RIGHT:
> +		return fb->format->char_per_block[plane_index];
> +	case READ_RIGHT_TO_LEFT:
> +		return -fb->format->char_per_block[plane_index];
> +	case READ_TOP_TO_BOTTOM:
> +		return (int)fb->pitches[plane_index];
> +	case READ_BOTTOM_TO_TOP:
> +		return -(int)fb->pitches[plane_index];
> +	}
> +
> +	return 0;
> +}
> +
>   static void *get_packed_src_addr(const struct vkms_frame_info *frame_info, int y,
>   				 int plane_index)
>   {
>