drm/format-helper: Move helpers for pixel conversion to header file

The DRM draw helpers contain format-conversion helpers that operate
on individual pixels. Move them into an internal header file and adopt
them as individual API. Update the draw code accordingly. The pixel
helpers will also be useful for other format conversion helpers.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20250328141709.217283-2-tzimmermann@suse.de

1 files changed, 119 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_format_internal.h b/drivers/gpu/drm/drm_format_internal.h
new file mode 100644
index 000000000000..5f82f0b9c8e8
--- /dev/null
+++ b/drivers/gpu/drm/drm_format_internal.h
@@ -0,0 +1,119 @@
+/* SPDX-License-Identifier: GPL-2.0 or MIT */
+
+#ifndef DRM_FORMAT_INTERNAL_H
+#define DRM_FORMAT_INTERNAL_H
+
+#include <linux/bits.h>
+#include <linux/types.h>
+
+/*
+ * Each pixel-format conversion helper takes a raw pixel in a
+ * specific input format and returns a raw pixel in a specific
+ * output format. All pixels are in little-endian byte order.
+ *
+ * Function names are
+ *
+ *   drm_pixel_<input>_to_<output>_<algorithm>()
+ *
+ * where <input> and <output> refer to pixel formats. The
+ * <algorithm> is optional and hints to the method used for the
+ * conversion. Helpers with no algorithm given apply pixel-bit
+ * shifting.
+ *
+ * The argument type is u32. We expect this to be wide enough to
+ * hold all conversion input from 32-bit RGB to any output format.
+ * The Linux kernel should avoid format conversion for anything
+ * but XRGB8888 input data. Converting from other format can still
+ * be acceptable in some cases.
+ *
+ * The return type is u32. It is wide enough to hold all conversion
+ * output from XRGB8888. For output formats wider than 32 bit, a
+ * return type of u64 would be acceptable.
+ */
+
+/*
+ * Conversions from XRGB8888
+ */
+
+static inline u32 drm_pixel_xrgb8888_to_rgb565(u32 pix)
+{
+	return ((pix & 0x00f80000) >> 8) |
+	       ((pix & 0x0000fc00) >> 5) |
+	       ((pix & 0x000000f8) >> 3);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_rgbx5551(u32 pix)
+{
+	return ((pix & 0x00f80000) >> 8) |
+	       ((pix & 0x0000f800) >> 5) |
+	       ((pix & 0x000000f8) >> 2);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_rgba5551(u32 pix)
+{
+	return drm_pixel_xrgb8888_to_rgbx5551(pix) |
+	       BIT(0); /* set alpha bit */
+}
+
+static inline u32 drm_pixel_xrgb8888_to_xrgb1555(u32 pix)
+{
+	return ((pix & 0x00f80000) >> 9) |
+	       ((pix & 0x0000f800) >> 6) |
+	       ((pix & 0x000000f8) >> 3);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_argb1555(u32 pix)
+{
+	return BIT(15) | /* set alpha bit */
+	       drm_pixel_xrgb8888_to_xrgb1555(pix);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_argb8888(u32 pix)
+{
+	return GENMASK(31, 24) | /* fill alpha bits */
+	       pix;
+}
+
+static inline u32 drm_pixel_xrgb8888_to_xbgr8888(u32 pix)
+{
+	return ((pix & 0xff000000)) | /* also copy filler bits */
+	       ((pix & 0x00ff0000) >> 16) |
+	       ((pix & 0x0000ff00)) |
+	       ((pix & 0x000000ff) << 16);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_abgr8888(u32 pix)
+{
+	return GENMASK(31, 24) | /* fill alpha bits */
+	       drm_pixel_xrgb8888_to_xbgr8888(pix);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_xrgb2101010(u32 pix)
+{
+	pix = ((pix & 0x000000ff) << 2) |
+	      ((pix & 0x0000ff00) << 4) |
+	      ((pix & 0x00ff0000) << 6);
+	return pix | ((pix >> 8) & 0x00300c03);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_argb2101010(u32 pix)
+{
+	return GENMASK(31, 30) | /* set alpha bits */
+	       drm_pixel_xrgb8888_to_xrgb2101010(pix);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_xbgr2101010(u32 pix)
+{
+	pix = ((pix & 0x00ff0000) >> 14) |
+	      ((pix & 0x0000ff00) << 4) |
+	      ((pix & 0x000000ff) << 22);
+	return pix | ((pix >> 8) & 0x00300c03);
+}
+
+static inline u32 drm_pixel_xrgb8888_to_abgr2101010(u32 pix)
+{
+	return GENMASK(31, 30) | /* set alpha bits */
+	       drm_pixel_xrgb8888_to_xbgr2101010(pix);
+}
+
+#endif