[linux-2.6-block.git] / drivers / gpu / drm / drm_format_helper.c

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright (C) 2016 Noralf Trønnes
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/io.h>

#include <drm/drm_format_helper.h>
#include <drm/drm_framebuffer.h>
#include <drm/drm_fourcc.h>
#include <drm/drm_rect.h>

static unsigned int clip_offset(struct drm_rect *clip,
				unsigned int pitch, unsigned int cpp)
{
	return clip->y1 * pitch + clip->x1 * cpp;
}

/**
 * drm_fb_memcpy - Copy clip buffer
 * @dst: Destination buffer
 * @vaddr: Source buffer
 * @fb: DRM framebuffer
 * @clip: Clip rectangle area to copy
 *
 * This function does not apply clipping on dst, i.e. the destination
 * is a small buffer containing the clip rect only.
 */
void drm_fb_memcpy(void *dst, void *vaddr, struct drm_framebuffer *fb,
		   struct drm_rect *clip)
{
	unsigned int cpp = fb->format->cpp[0];
	size_t len = (clip->x2 - clip->x1) * cpp;
	unsigned int y, lines = clip->y2 - clip->y1;

	vaddr += clip_offset(clip, fb->pitches[0], cpp);
	for (y = 0; y < lines; y++) {
		memcpy(dst, vaddr, len);
		vaddr += fb->pitches[0];
		dst += len;
	}
}
EXPORT_SYMBOL(drm_fb_memcpy);

/**
 * drm_fb_memcpy_dstclip - Copy clip buffer
 * @dst: Destination buffer (iomem)
 * @vaddr: Source buffer
 * @fb: DRM framebuffer
 * @clip: Clip rectangle area to copy
 *
 * 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_memcpy_dstclip(void __iomem *dst, void *vaddr,
			   struct drm_framebuffer *fb,
			   struct drm_rect *clip)
{
	unsigned int cpp = fb->format->cpp[0];
	unsigned int offset = clip_offset(clip, fb->pitches[0], cpp);
	size_t len = (clip->x2 - clip->x1) * cpp;
	unsigned int y, lines = clip->y2 - clip->y1;

	vaddr += offset;
	dst += offset;
	for (y = 0; y < lines; y++) {
		memcpy_toio(dst, vaddr, len);
		vaddr += fb->pitches[0];
		dst += fb->pitches[0];
	}
}
EXPORT_SYMBOL(drm_fb_memcpy_dstclip);

/**
 * drm_fb_swab16 - Swap bytes into clip buffer
 * @dst: RGB565 destination buffer
 * @vaddr: RGB565 source buffer
 * @fb: DRM framebuffer
 * @clip: Clip rectangle area to copy
 */
void drm_fb_swab16(u16 *dst, void *vaddr, struct drm_framebuffer *fb,
		   struct drm_rect *clip)
{
	size_t len = (clip->x2 - clip->x1) * sizeof(u16);
	unsigned int x, y;
	u16 *src, *buf;

	/*
	 * The cma memory is write-combined so reads are uncached.
	 * Speed up by fetching one line at a time.
	 */
	buf = kmalloc(len, GFP_KERNEL);
	if (!buf)
		return;

	for (y = clip->y1; y < clip->y2; y++) {
		src = vaddr + (y * fb->pitches[0]);
		src += clip->x1;
		memcpy(buf, src, len);
		src = buf;
		for (x = clip->x1; x < clip->x2; x++)
			*dst++ = swab16(*src++);
	}

	kfree(buf);
}
EXPORT_SYMBOL(drm_fb_swab16);

static void drm_fb_xrgb8888_to_rgb565_line(u16 *dbuf, u32 *sbuf,
					   unsigned int pixels,
					   bool swab)
{
	unsigned int x;
	u16 val16;

	for (x = 0; x < pixels; x++) {
		val16 = ((sbuf[x] & 0x00F80000) >> 8) |
			((sbuf[x] & 0x0000FC00) >> 5) |
			((sbuf[x] & 0x000000F8) >> 3);
		if (swab)
			dbuf[x] = swab16(val16);
		else
			dbuf[x] = val16;
	}
}

/**
 * drm_fb_xrgb8888_to_rgb565 - Convert XRGB8888 to RGB565 clip buffer
 * @dst: RGB565 destination buffer
 * @vaddr: XRGB8888 source buffer
 * @fb: DRM framebuffer
 * @clip: Clip rectangle area to copy
 * @swab: Swap bytes
 *
 * Drivers can use this function for RGB565 devices that don't natively
 * support XRGB8888.
 *
 * This function does not apply clipping on dst, i.e. the destination
 * is a small buffer containing the clip rect only.
 */
void drm_fb_xrgb8888_to_rgb565(void *dst, void *vaddr,
			       struct drm_framebuffer *fb,
			       struct drm_rect *clip, bool swab)
{
	size_t linepixels = clip->x2 - clip->x1;
	size_t src_len = linepixels * sizeof(u32);
	size_t dst_len = linepixels * sizeof(u16);
	unsigned y, lines = clip->y2 - clip->y1;
	void *sbuf;

	/*
	 * The cma memory is write-combined so reads are uncached.
	 * Speed up by fetching one line at a time.
	 */
	sbuf = kmalloc(src_len, GFP_KERNEL);
	if (!sbuf)
		return;

	vaddr += clip_offset(clip, fb->pitches[0], sizeof(u32));
	for (y = 0; y < lines; y++) {
		memcpy(sbuf, vaddr, src_len);
		drm_fb_xrgb8888_to_rgb565_line(dst, sbuf, linepixels, swab);
		vaddr += fb->pitches[0];
		dst += dst_len;
	}

	kfree(sbuf);
}
EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb565);

/**
 * drm_fb_xrgb8888_to_rgb565_dstclip - Convert XRGB8888 to RGB565 clip buffer
 * @dst: RGB565 destination buffer (iomem)
 * @dst_pitch: destination buffer pitch
 * @vaddr: XRGB8888 source buffer
 * @fb: DRM framebuffer
 * @clip: Clip rectangle area to copy
 * @swab: Swap bytes
 *
 * Drivers can use this function for RGB565 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_rgb565_dstclip(void __iomem *dst, unsigned int dst_pitch,
				       void *vaddr, struct drm_framebuffer *fb,
				       struct drm_rect *clip, bool swab)
{
	size_t linepixels = clip->x2 - clip->x1;
	size_t dst_len = linepixels * sizeof(u16);
	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_rgb565_line(dbuf, vaddr, linepixels, swab);
		memcpy_toio(dst, dbuf, dst_len);
		vaddr += fb->pitches[0];
		dst += dst_len;
	}

	kfree(dbuf);
}
EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb565_dstclip);

static void drm_fb_xrgb8888_to_rgb888_line(u8 *dbuf, u32 *sbuf,
					   unsigned int pixels)
{
	unsigned int x;

	for (x = 0; x < pixels; x++) {
		*dbuf++ = (sbuf[x] & 0x000000FF) >>  0;
		*dbuf++ = (sbuf[x] & 0x0000FF00) >>  8;
		*dbuf++ = (sbuf[x] & 0x00FF0000) >> 16;
	}
}

/**
 * drm_fb_xrgb8888_to_rgb888_dstclip - Convert XRGB8888 to RGB888 clip buffer
 * @dst: RGB565 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 RGB888 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_rgb888_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 * 3;
	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_rgb888_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
 * @vaddr: XRGB8888 source buffer
 * @fb: DRM framebuffer
 * @clip: Clip rectangle area to copy
 *
 * Drm doesn't have native monochrome or grayscale support.
 * Such drivers can announce the commonly supported XR24 format to userspace
 * and use this function to convert to the native format.
 *
 * Monochrome drivers will use the most significant bit,
 * where 1 means foreground color and 0 background color.
 *
 * ITU BT.601 is used for the RGB -> luma (brightness) conversion.
 */
void drm_fb_xrgb8888_to_gray8(u8 *dst, void *vaddr, struct drm_framebuffer *fb,
			       struct drm_rect *clip)
{
	unsigned int len = (clip->x2 - clip->x1) * sizeof(u32);
	unsigned int x, y;
	void *buf;
	u32 *src;

	if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
		return;
	/*
	 * The cma memory is write-combined so reads are uncached.
	 * Speed up by fetching one line at a time.
	 */
	buf = kmalloc(len, GFP_KERNEL);
	if (!buf)
		return;

	for (y = clip->y1; y < clip->y2; y++) {
		src = vaddr + (y * fb->pitches[0]);
		src += clip->x1;
		memcpy(buf, src, len);
		src = buf;
		for (x = clip->x1; x < clip->x2; x++) {
			u8 r = (*src & 0x00ff0000) >> 16;
			u8 g = (*src & 0x0000ff00) >> 8;
			u8 b =  *src & 0x000000ff;

			/* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
			*dst++ = (3 * r + 6 * g + b) / 10;
			src++;
		}
	}

	kfree(buf);
}
EXPORT_SYMBOL(drm_fb_xrgb8888_to_gray8);
Commit	Line	Data
7415287e GH	1	/* SPDX-License-Identifier: GPL-2.0 */
	2	/*
	3	* Copyright (C) 2016 Noralf Trønnes
	4	*
	5	* This program is free software; you can redistribute it and/or modify
	6	* it under the terms of the GNU General Public License as published by
	7	* the Free Software Foundation; either version 2 of the License, or
	8	* (at your option) any later version.
	9	*/
	10
	11	#include <linux/module.h>
	12	#include <linux/slab.h>
bf4f6d16	13	#include <linux/io.h>
7415287e GH	14
	15	#include <drm/drm_format_helper.h>
	16	#include <drm/drm_framebuffer.h>
	17	#include <drm/drm_fourcc.h>
	18	#include <drm/drm_rect.h>
	19
bf4f6d16 GH	20	static unsigned int clip_offset(struct drm_rect *clip,
bf4f6d16 GH	21	unsigned int pitch, unsigned int cpp)
26f024f5	22	{
bf4f6d16	23	return clip->y1 * pitch + clip->x1 * cpp;
26f024f5 GH	24	}
26f024f5 GH	25
7415287e GH	26	/**
	27	* drm_fb_memcpy - Copy clip buffer
	28	* @dst: Destination buffer
	29	* @vaddr: Source buffer
	30	* @fb: DRM framebuffer
	31	* @clip: Clip rectangle area to copy
26f024f5 GH	32	*
	33	* This function does not apply clipping on dst, i.e. the destination
	34	* is a small buffer containing the clip rect only.
7415287e GH	35	*/
	36	void drm_fb_memcpy(void dst, void vaddr, struct drm_framebuffer *fb,
	37	struct drm_rect *clip)
	38	{
b0f986b4	39	unsigned int cpp = fb->format->cpp[0];
7415287e	40	size_t len = (clip->x2 - clip->x1) * cpp;
bf4f6d16	41	unsigned int y, lines = clip->y2 - clip->y1;
7415287e	42
bf4f6d16 GH	43	vaddr += clip_offset(clip, fb->pitches[0], cpp);
	44	for (y = 0; y < lines; y++) {
	45	memcpy(dst, vaddr, len);
	46	vaddr += fb->pitches[0];
	47	dst += len;
	48	}
7415287e GH	49	}
	50	EXPORT_SYMBOL(drm_fb_memcpy);
	51
26f024f5 GH	52	/**
26f024f5 GH	53	* drm_fb_memcpy_dstclip - Copy clip buffer
bf4f6d16	54	* @dst: Destination buffer (iomem)
26f024f5 GH	55	* @vaddr: Source buffer
	56	* @fb: DRM framebuffer
	57	* @clip: Clip rectangle area to copy
	58	*
	59	* This function applies clipping on dst, i.e. the destination is a
bf4f6d16	60	* full (iomem) framebuffer but only the clip rect content is copied over.
26f024f5	61	*/
bf4f6d16 GH	62	void drm_fb_memcpy_dstclip(void __iomem dst, void vaddr,
bf4f6d16 GH	63	struct drm_framebuffer *fb,
26f024f5 GH	64	struct drm_rect *clip)
26f024f5 GH	65	{
b0f986b4	66	unsigned int cpp = fb->format->cpp[0];
bf4f6d16	67	unsigned int offset = clip_offset(clip, fb->pitches[0], cpp);
26f024f5	68	size_t len = (clip->x2 - clip->x1) * cpp;
bf4f6d16	69	unsigned int y, lines = clip->y2 - clip->y1;
26f024f5	70
bf4f6d16 GH	71	vaddr += offset;
	72	dst += offset;
	73	for (y = 0; y < lines; y++) {
	74	memcpy_toio(dst, vaddr, len);
	75	vaddr += fb->pitches[0];
	76	dst += fb->pitches[0];
	77	}
26f024f5 GH	78	}
	79	EXPORT_SYMBOL(drm_fb_memcpy_dstclip);
	80
7415287e GH	81	/**
	82	* drm_fb_swab16 - Swap bytes into clip buffer
	83	* @dst: RGB565 destination buffer
	84	* @vaddr: RGB565 source buffer
	85	* @fb: DRM framebuffer
	86	* @clip: Clip rectangle area to copy
	87	*/
	88	void drm_fb_swab16(u16 dst, void vaddr, struct drm_framebuffer *fb,
	89	struct drm_rect *clip)
	90	{
	91	size_t len = (clip->x2 - clip->x1) * sizeof(u16);
	92	unsigned int x, y;
	93	u16 src, buf;
	94
	95	/*
	96	* The cma memory is write-combined so reads are uncached.
	97	* Speed up by fetching one line at a time.
	98	*/
	99	buf = kmalloc(len, GFP_KERNEL);
	100	if (!buf)
	101	return;
	102
	103	for (y = clip->y1; y < clip->y2; y++) {
	104	src = vaddr + (y * fb->pitches[0]);
	105	src += clip->x1;
	106	memcpy(buf, src, len);
	107	src = buf;
	108	for (x = clip->x1; x < clip->x2; x++)
	109	dst++ = swab16(src++);
	110	}
	111
	112	kfree(buf);
	113	}
	114	EXPORT_SYMBOL(drm_fb_swab16);
	115
d653bd39 GH	116	static void drm_fb_xrgb8888_to_rgb565_line(u16 dbuf, u32 sbuf,
	117	unsigned int pixels,
	118	bool swab)
7415287e	119	{
d653bd39 GH	120	unsigned int x;
	121	u16 val16;
	122
	123	for (x = 0; x < pixels; x++) {
	124	val16 = ((sbuf[x] & 0x00F80000) >> 8) \|
	125	((sbuf[x] & 0x0000FC00) >> 5) \|
	126	((sbuf[x] & 0x000000F8) >> 3);
	127	if (swab)
	128	dbuf[x] = swab16(val16);
	129	else
	130	dbuf[x] = val16;
7415287e	131	}
bcc44420 GH	132	}
	133
	134	/**
	135	* drm_fb_xrgb8888_to_rgb565 - Convert XRGB8888 to RGB565 clip buffer
	136	* @dst: RGB565 destination buffer
	137	* @vaddr: XRGB8888 source buffer
	138	* @fb: DRM framebuffer
	139	* @clip: Clip rectangle area to copy
d653bd39	140	* @swab: Swap bytes
bcc44420 GH	141	*
	142	* Drivers can use this function for RGB565 devices that don't natively
	143	* support XRGB8888.
	144	*
	145	* This function does not apply clipping on dst, i.e. the destination
	146	* is a small buffer containing the clip rect only.
	147	*/
	148	void drm_fb_xrgb8888_to_rgb565(void dst, void vaddr,
	149	struct drm_framebuffer *fb,
d653bd39	150	struct drm_rect *clip, bool swab)
bcc44420	151	{
d653bd39 GH	152	size_t linepixels = clip->x2 - clip->x1;
	153	size_t src_len = linepixels * sizeof(u32);
	154	size_t dst_len = linepixels * sizeof(u16);
	155	unsigned y, lines = clip->y2 - clip->y1;
	156	void *sbuf;
	157
	158	/*
	159	* The cma memory is write-combined so reads are uncached.
	160	* Speed up by fetching one line at a time.
	161	*/
	162	sbuf = kmalloc(src_len, GFP_KERNEL);
	163	if (!sbuf)
	164	return;
	165
	166	vaddr += clip_offset(clip, fb->pitches[0], sizeof(u32));
	167	for (y = 0; y < lines; y++) {
	168	memcpy(sbuf, vaddr, src_len);
	169	drm_fb_xrgb8888_to_rgb565_line(dst, sbuf, linepixels, swab);
	170	vaddr += fb->pitches[0];
	171	dst += dst_len;
	172	}
	173
	174	kfree(sbuf);
7415287e GH	175	}
	176	EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb565);
	177
bcc44420 GH	178	/**
bcc44420 GH	179	* drm_fb_xrgb8888_to_rgb565_dstclip - Convert XRGB8888 to RGB565 clip buffer
d653bd39	180	* @dst: RGB565 destination buffer (iomem)
bcc44420 GH	181	* @dst_pitch: destination buffer pitch
	182	* @vaddr: XRGB8888 source buffer
	183	* @fb: DRM framebuffer
	184	* @clip: Clip rectangle area to copy
d653bd39	185	* @swab: Swap bytes
bcc44420 GH	186	*
	187	* Drivers can use this function for RGB565 devices that don't natively
	188	* support XRGB8888.
	189	*
	190	* This function applies clipping on dst, i.e. the destination is a
d653bd39	191	* full (iomem) framebuffer but only the clip rect content is copied over.
bcc44420	192	*/
d653bd39	193	void drm_fb_xrgb8888_to_rgb565_dstclip(void __iomem *dst, unsigned int dst_pitch,
bcc44420	194	void vaddr, struct drm_framebuffer fb,
d653bd39	195	struct drm_rect *clip, bool swab)
bcc44420	196	{
d653bd39 GH	197	size_t linepixels = clip->x2 - clip->x1;
	198	size_t dst_len = linepixels * sizeof(u16);
	199	unsigned y, lines = clip->y2 - clip->y1;
	200	void *dbuf;
	201
	202	dbuf = kmalloc(dst_len, GFP_KERNEL);
	203	if (!dbuf)
	204	return;
	205
	206	vaddr += clip_offset(clip, fb->pitches[0], sizeof(u32));
	207	dst += clip_offset(clip, dst_pitch, sizeof(u16));
	208	for (y = 0; y < lines; y++) {
	209	drm_fb_xrgb8888_to_rgb565_line(dbuf, vaddr, linepixels, swab);
	210	memcpy_toio(dst, dbuf, dst_len);
	211	vaddr += fb->pitches[0];
	212	dst += dst_len;
	213	}
	214
	215	kfree(dbuf);
bcc44420 GH	216	}
	217	EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb565_dstclip);
	218
5c5373b5 GH	219	static void drm_fb_xrgb8888_to_rgb888_line(u8 dbuf, u32 sbuf,
5c5373b5 GH	220	unsigned int pixels)
ec3de7a4	221	{
5c5373b5	222	unsigned int x;
ec3de7a4	223
5c5373b5 GH	224	for (x = 0; x < pixels; x++) {
	225	*dbuf++ = (sbuf[x] & 0x000000FF) >> 0;
	226	*dbuf++ = (sbuf[x] & 0x0000FF00) >> 8;
	227	*dbuf++ = (sbuf[x] & 0x00FF0000) >> 16;
ec3de7a4	228	}
ec3de7a4 GH	229	}
	230
	231	/**
	232	* drm_fb_xrgb8888_to_rgb888_dstclip - Convert XRGB8888 to RGB888 clip buffer
79b97973	233	* @dst: RGB565 destination buffer (iomem)
ec3de7a4 GH	234	* @dst_pitch: destination buffer pitch
	235	* @vaddr: XRGB8888 source buffer
	236	* @fb: DRM framebuffer
	237	* @clip: Clip rectangle area to copy
ec3de7a4 GH	238	*
	239	* Drivers can use this function for RGB888 devices that don't natively
	240	* support XRGB8888.
	241	*
	242	* This function applies clipping on dst, i.e. the destination is a
79b97973	243	* full (iomem) framebuffer but only the clip rect content is copied over.
ec3de7a4	244	*/
79b97973	245	void drm_fb_xrgb8888_to_rgb888_dstclip(void __iomem *dst, unsigned int dst_pitch,
ec3de7a4 GH	246	void vaddr, struct drm_framebuffer fb,
	247	struct drm_rect *clip)
	248	{
5c5373b5 GH	249	size_t linepixels = clip->x2 - clip->x1;
	250	size_t dst_len = linepixels * 3;
	251	unsigned y, lines = clip->y2 - clip->y1;
	252	void *dbuf;
ec3de7a4	253
5c5373b5 GH	254	dbuf = kmalloc(dst_len, GFP_KERNEL);
	255	if (!dbuf)
	256	return;
	257
	258	vaddr += clip_offset(clip, fb->pitches[0], sizeof(u32));
	259	dst += clip_offset(clip, dst_pitch, sizeof(u16));
	260	for (y = 0; y < lines; y++) {
	261	drm_fb_xrgb8888_to_rgb888_line(dbuf, vaddr, linepixels);
	262	memcpy_toio(dst, dbuf, dst_len);
	263	vaddr += fb->pitches[0];
	264	dst += dst_len;
	265	}
	266
	267	kfree(dbuf);
ec3de7a4 GH	268	}
	269	EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb888_dstclip);
	270
7415287e GH	271	/**
	272	* drm_fb_xrgb8888_to_gray8 - Convert XRGB8888 to grayscale
	273	* @dst: 8-bit grayscale destination buffer
	274	* @vaddr: XRGB8888 source buffer
	275	* @fb: DRM framebuffer
	276	* @clip: Clip rectangle area to copy
	277	*
	278	* Drm doesn't have native monochrome or grayscale support.
	279	* Such drivers can announce the commonly supported XR24 format to userspace
	280	* and use this function to convert to the native format.
	281	*
	282	* Monochrome drivers will use the most significant bit,
	283	* where 1 means foreground color and 0 background color.
	284	*
	285	* ITU BT.601 is used for the RGB -> luma (brightness) conversion.
	286	*/
	287	void drm_fb_xrgb8888_to_gray8(u8 dst, void vaddr, struct drm_framebuffer *fb,
	288	struct drm_rect *clip)
	289	{
	290	unsigned int len = (clip->x2 - clip->x1) * sizeof(u32);
	291	unsigned int x, y;
	292	void *buf;
	293	u32 *src;
	294
	295	if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
	296	return;
	297	/*
	298	* The cma memory is write-combined so reads are uncached.
	299	* Speed up by fetching one line at a time.
	300	*/
	301	buf = kmalloc(len, GFP_KERNEL);
	302	if (!buf)
	303	return;
	304
	305	for (y = clip->y1; y < clip->y2; y++) {
	306	src = vaddr + (y * fb->pitches[0]);
	307	src += clip->x1;
	308	memcpy(buf, src, len);
	309	src = buf;
	310	for (x = clip->x1; x < clip->x2; x++) {
	311	u8 r = (*src & 0x00ff0000) >> 16;
	312	u8 g = (*src & 0x0000ff00) >> 8;
	313	u8 b = *src & 0x000000ff;
	314
	315	/* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
	316	dst++ = (3 r + 6 * g + b) / 10;
	317	src++;
	318	}
	319	}
	320
	321	kfree(buf);
	322	}
	323	EXPORT_SYMBOL(drm_fb_xrgb8888_to_gray8);
	324