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

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

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.
+ */
+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
+ */
+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)
 {

-- 
2.43.0