path: root/drivers/gpu/drm/vkms/vkms_composer.c

// SPDX-License-Identifier: GPL-2.0+

#include <linux/crc32.h>

#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
#include <drm/drm_blend.h>
#include <drm/drm_fourcc.h>
#include <drm/drm_fixed.h>
#include <drm/drm_gem_framebuffer_helper.h>
#include <drm/drm_vblank.h>
#include <linux/minmax.h>

#include "vkms_drv.h"

static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)
{
	u32 new_color;

	new_color = (src * 0xffff + dst * (0xffff - alpha));

	return DIV_ROUND_CLOSEST(new_color, 0xffff);
}

/**
 * pre_mul_alpha_blend - alpha blending equation
 * @stage_buffer: The line with the pixels from src_plane
 * @output_buffer: A line buffer that receives all the blends output
 * @x_start: The start offset
 * @pixel_count: The number of pixels to blend
 *
 * The pixels [@x_start;@x_start+@pixel_count) in stage_buffer are blended at
 * [@x_start;@x_start+@pixel_count) in output_buffer.
 *
 * The current DRM assumption is that pixel color values have been already
 * pre-multiplied with the alpha channel values. See more
 * drm_plane_create_blend_mode_property(). Also, this formula assumes a
 * completely opaque background.
 */
static void pre_mul_alpha_blend(const struct line_buffer *stage_buffer,
				struct line_buffer *output_buffer, int x_start, int pixel_count)
{
	struct pixel_argb_u16 *out = &output_buffer->pixels[x_start];
	const struct pixel_argb_u16 *in = &stage_buffer->pixels[x_start];

	for (int i = 0; i < pixel_count; i++) {
		out[i].a = (u16)0xffff;
		out[i].r = pre_mul_blend_channel(in[i].r, out[i].r, in[i].a);
		out[i].g = pre_mul_blend_channel(in[i].g, out[i].g, in[i].a);
		out[i].b = pre_mul_blend_channel(in[i].b, out[i].b, in[i].a);
	}
}


static void fill_background(const struct pixel_argb_u16 *background_color,
			    struct line_buffer *output_buffer)
{
	for (size_t i = 0; i < output_buffer->n_pixels; i++)
		output_buffer->pixels[i] = *background_color;
}

// lerp(a, b, t) = a + (b - a) * t
static u16 lerp_u16(u16 a, u16 b, s64 t)
{
	s64 a_fp = drm_int2fixp(a);
	s64 b_fp = drm_int2fixp(b);

	s64 delta = drm_fixp_mul(b_fp - a_fp, t);

	return drm_fixp2int_round(a_fp + delta);
}

static s64 get_lut_index(const struct vkms_color_lut *lut, u16 channel_value)
{
	s64 color_channel_fp = drm_int2fixp(channel_value);

	return drm_fixp_mul(color_channel_fp, lut->channel_value2index_ratio);
}

/*
 * This enum is related to the positions of the variables inside
 * `struct drm_color_lut`, so the order of both needs to be the same.
 */
enum lut_channel {
	LUT_RED = 0,
	LUT_GREEN,
	LUT_BLUE,
	LUT_RESERVED
};

static u16 apply_lut_to_channel_value(const struct vkms_color_lut *lut, u16 channel_value,
				      enum lut_channel channel)
{
	s64 lut_index = get_lut_index(lut, channel_value);
	u16 *floor_lut_value, *ceil_lut_value;
	u16 floor_channel_value, ceil_channel_value;

	/*
	 * This checks if `struct drm_color_lut` has any gap added by the compiler
	 * between the struct fields.
	 */
	static_assert(sizeof(struct drm_color_lut) == sizeof(__u16) * 4);

	floor_lut_value = (__u16 *)&lut->base[drm_fixp2int(lut_index)];
	if (drm_fixp2int(lut_index) == (lut->lut_length - 1))
		/* We're at the end of the LUT array, use same value for ceil and floor */
		ceil_lut_value = floor_lut_value;
	else
		ceil_lut_value = (__u16 *)&lut->base[drm_fixp2int_ceil(lut_index)];

	floor_channel_value = floor_lut_value[channel];
	ceil_channel_value = ceil_lut_value[channel];

	return lerp_u16(floor_channel_value, ceil_channel_value,
			lut_index & DRM_FIXED_DECIMAL_MASK);
}

static void apply_lut(const struct vkms_crtc_state *crtc_state, struct line_buffer *output_buffer)
{
	if (!crtc_state->gamma_lut.base)
		return;

	if (!crtc_state->gamma_lut.lut_length)
		return;

	for (size_t x = 0; x < output_buffer->n_pixels; x++) {
		struct pixel_argb_u16 *pixel = &output_buffer->pixels[x];

		pixel->r = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->r, LUT_RED);
		pixel->g = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->g, LUT_GREEN);
		pixel->b = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->b, LUT_BLUE);
	}
}

/**
 * direction_for_rotation() - Get the correct reading direction for a given rotation
 *
 * @rotation: Rotation to analyze. It correspond the field @frame_info.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.
 */
static enum pixel_read_direction direction_for_rotation(unsigned int rotation)
{
	struct drm_rect tmp_a, tmp_b;
	int x, y;

	/*
	 * Points A and B are depicted as zero-size rectangles on the CRTC.
	 * The CRTC writing direction is from A to B. The plane reading direction
	 * is discovered by inverse-transforming A and B.
	 * The reading direction is computed by rotating the vector AB (top-left to top-right) in a
	 * 1x1 square.
	 */

	tmp_a = DRM_RECT_INIT(0, 0, 0, 0);
	tmp_b = DRM_RECT_INIT(1, 0, 0, 0);
	drm_rect_rotate_inv(&tmp_a, 1, 1, rotation);
	drm_rect_rotate_inv(&tmp_b, 1, 1, rotation);

	x = tmp_b.x1 - tmp_a.x1;
	y = tmp_b.y1 - tmp_a.y1;

	if (x == 1 && y == 0)
		return READ_LEFT_TO_RIGHT;
	else if (x == -1 && y == 0)
		return READ_RIGHT_TO_LEFT;
	else if (y == 1 && x == 0)
		return READ_TOP_TO_BOTTOM;
	else if (y == -1 && x == 0)
		return READ_BOTTOM_TO_TOP;

	WARN_ONCE(true, "The inverse of the rotation gives an incorrect direction.");
	return READ_LEFT_TO_RIGHT;
}

/**
 * clamp_line_coordinates() - Compute and clamp the coordinate to read and write during the blend
 * process.
 *
 * @direction: direction of the reading
 * @current_plane: current plane blended
 * @src_line: source line of the reading. Only the top-left coordinate is used. This rectangle
 * must be rotated and have a shape of 1*pixel_count if @direction is vertical and a shape of
 * pixel_count*1 if @direction is horizontal.
 * @src_x_start: x start coordinate for the line reading
 * @src_y_start: y start coordinate for the line reading
 * @dst_x_start: x coordinate to blend the read line
 * @pixel_count: number of pixels to blend
 *
 * This function is mainly a safety net to avoid reading outside the source buffer. As the
 * userspace should never ask to read outside the source plane, all the cases covered here should
 * be dead code.
 */
static void clamp_line_coordinates(enum pixel_read_direction direction,
				   const struct vkms_plane_state *current_plane,
				   const struct drm_rect *src_line, int *src_x_start,
				   int *src_y_start, int *dst_x_start, int *pixel_count)
{
	/* By default the start points are correct */
	*src_x_start = src_line->x1;
	*src_y_start = src_line->y1;
	*dst_x_start = current_plane->frame_info->dst.x1;

	/* Get the correct number of pixel to blend, it depends of the direction */
	switch (direction) {
	case READ_LEFT_TO_RIGHT:
	case READ_RIGHT_TO_LEFT:
		*pixel_count = drm_rect_width(src_line);
		break;
	case READ_BOTTOM_TO_TOP:
	case READ_TOP_TO_BOTTOM:
		*pixel_count = drm_rect_height(src_line);
		break;
	}

	/*
	 * Clamp the coordinates to avoid reading outside the buffer
	 *
	 * This is mainly a security check to avoid reading outside the buffer, the userspace
	 * should never request to read outside the source buffer.
	 */
	switch (direction) {
	case READ_LEFT_TO_RIGHT:
	case READ_RIGHT_TO_LEFT:
		if (*src_x_start < 0) {
			*pixel_count += *src_x_start;
			*dst_x_start -= *src_x_start;
			*src_x_start = 0;
		}
		if (*src_x_start + *pixel_count > current_plane->frame_info->fb->width)
			*pixel_count = max(0, (int)current_plane->frame_info->fb->width -
				*src_x_start);
		break;
	case READ_BOTTOM_TO_TOP:
	case READ_TOP_TO_BOTTOM:
		if (*src_y_start < 0) {
			*pixel_count += *src_y_start;
			*dst_x_start -= *src_y_start;
			*src_y_start = 0;
		}
		if (*src_y_start + *pixel_count > current_plane->frame_info->fb->height)
			*pixel_count = max(0, (int)current_plane->frame_info->fb->height -
				*src_y_start);
		break;
	}
}

/**
 * blend_line() - Blend a line from a plane to the output buffer
 *
 * @current_plane: current plane to work on
 * @y: line to write in the output buffer
 * @crtc_x_limit: width of the output buffer
 * @stage_buffer: temporary buffer to convert the pixel line from the source buffer
 * @output_buffer: buffer to blend the read line into.
 */
static void blend_line(struct vkms_plane_state *current_plane, int y,
		       int crtc_x_limit, struct line_buffer *stage_buffer,
		       struct line_buffer *output_buffer)
{
	int src_x_start, src_y_start, dst_x_start, pixel_count;
	struct drm_rect dst_line, tmp_src, src_line;

	/* Avoid rendering useless lines */
	if (y < current_plane->frame_info->dst.y1 ||