drm/format-helper: Add drm_fb_xrgb8888_to_xrgb2101010_dstclip()

Add XRGB8888 emulation support for devices that can only do XRGB2101010.

This is chiefly useful for simpledrm on Apple devices where the
bootloader-provided framebuffer is 10-bit.

Signed-off-by: Hector Martin <marcan@marcan.st>

drivers/gpu/drm/drm_format_helper.c

@@ -378,6 +378,60 @@ void drm_fb_xrgb8888_to_rgb888_dstclip(void __iomem *dst, unsigned int dst_pitch
 }
 EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb888_dstclip);
 
+static void drm_fb_xrgb8888_to_xrgb2101010_line(u32 *dbuf, u32 *sbuf,
+						unsigned int pixels)
+{
+	unsigned int x;
+
+	for (x = 0; x < pixels; x++) {
+		*dbuf++ = ((sbuf[x] & 0x000000FF) << 2) |
+			  ((sbuf[x] & 0x0000FF00) << 4) |
+			  ((sbuf[x] & 0x00FF0000) << 6);
+	}
+}
+
+/**
+ * drm_fb_xrgb8888_to_xrgb2101010_dstclip - Convert XRGB8888 to XRGB2101010 clip
+ * buffer
+ * @dst: XRGB2101010 destination buffer (iomem)
+ * @dst_pitch: destination buffer pitch
+ * @vaddr: XRGB8888 source buffer
+ * @fb: DRM framebuffer
+ * @clip: Clip rectangle area to copy
+ *
+ * Drivers can use this function for XRGB2101010 devices that don't natively
+ * support XRGB8888.
+ *
+ * This function applies clipping on dst, i.e. the destination is a
+ * full (iomem) framebuffer but only the clip rect content is copied over.
+ */
+void drm_fb_xrgb8888_to_xrgb2101010_dstclip(void __iomem *dst,
+					    unsigned int dst_pitch, void *vaddr,
+					    struct drm_framebuffer *fb,
+					    struct drm_rect *clip)
+{
+	size_t linepixels = clip->x2 - clip->x1;
+	size_t dst_len = linepixels * 4;
+	unsigned y, lines = clip->y2 - clip->y1;
+	void *dbuf;
+
+	dbuf = kmalloc(dst_len, GFP_KERNEL);
+	if (!dbuf)
+		return;
+
+	vaddr += clip_offset(clip, fb->pitches[0], sizeof(u32));
+	dst += clip_offset(clip, dst_pitch, sizeof(u16));
+	for (y = 0; y < lines; y++) {
+		drm_fb_xrgb8888_to_xrgb2101010_line(dbuf, vaddr, linepixels);
+		memcpy_toio(dst, dbuf, dst_len);
+		vaddr += fb->pitches[0];
+		dst += dst_len;
+	}
+
+	kfree(dbuf);
+}
+EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb888_dstclip);
+
 /**
  * drm_fb_xrgb8888_to_gray8 - Convert XRGB8888 to grayscale
  * @dst: 8-bit grayscale destination buffer
@@ -464,6 +518,10 @@ int drm_fb_blit_rect_dstclip(void __iomem *dst, unsigned int dst_pitch,
 		fb_format = DRM_FORMAT_XRGB8888;
 	if (dst_format == DRM_FORMAT_ARGB8888)
 		dst_format = DRM_FORMAT_XRGB8888;
+	if (fb_format == DRM_FORMAT_ARGB2101010)
+		fb_format = DRM_FORMAT_XRGB2101010;
+	if (dst_format == DRM_FORMAT_ARGB2101010)
+		dst_format = DRM_FORMAT_XRGB2101010;
 
 	if (dst_format == fb_format) {
 		drm_fb_memcpy_dstclip(dst, dst_pitch, vmap, fb, clip);
@@ -482,6 +540,12 @@ int drm_fb_blit_rect_dstclip(void __iomem *dst, unsigned int dst_pitch,
 							  vmap, fb, clip);
 			return 0;
 		}
+	} else if (dst_format == DRM_FORMAT_XRGB2101010) {
+		if (fb_format == DRM_FORMAT_XRGB8888) {
+			drm_fb_xrgb8888_to_xrgb2101010_dstclip(dst, dst_pitch,
+							       vmap, fb, clip);
+			return 0;
+		}
 	}
 
 	return -EINVAL;