[PATCH 2/7] drm/format-helper: Add drm_fb_xrgb8888_to_rgb332()

[Noralf Trønnes]

Den 17.08.2021 15.56, skrev Daniel Vetter:
> On Tue, Aug 17, 2021 at 02:29:12PM +0200, Noralf Trønnes wrote:
>> Add XRGB8888 emulation support for devices that can only do RGB332.
>>
>> Cc: Thomas Zimmermann <tzimmermann at suse.de>
>> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
>> ---
>>  drivers/gpu/drm/drm_format_helper.c | 47 +++++++++++++++++++++++++++++
>>  include/drm/drm_format_helper.h     |  2 ++
>>  2 files changed, 49 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
>> index 5231104b1498..53b426da7467 100644
>> --- a/drivers/gpu/drm/drm_format_helper.c
>> +++ b/drivers/gpu/drm/drm_format_helper.c
>> @@ -135,6 +135,53 @@ void drm_fb_swab(void *dst, void *src, struct drm_framebuffer *fb,
>>  }
>>  EXPORT_SYMBOL(drm_fb_swab);
>>  
>> +static void drm_fb_xrgb8888_to_rgb332_line(u8 *dbuf, u32 *sbuf, unsigned int pixels)
>> +{
>> +	unsigned int x;
>> +
>> +	for (x = 0; x < pixels; x++)
>> +		dbuf[x] = ((sbuf[x] & 0x00e00000) >> 16) |
> 
> I think for 2/3 bits correct rounding would be useful, not just masking.
> i.e. before you shift add 0x00100000 here, and similar below.
> 

Math isn't my strongest side and my brain failed to turn this into code.

> Also I just realized we've totally ignored endianess on these, which is
> not great, because strictly speaking all the drm_fourcc codes should be
> little endian. But I'm also not sure that's worth fixing ...
> 

Is it as simple as using le32_to_cpu()?

static void drm_fb_xrgb8888_to_rgb332_line(u8 *dbuf, __le32 *sbuf,
unsigned int pixels)
{
	unsigned int x;
	u32 pix;

	for (x = 0; x < pixels; x++) {
		pix = le32_to_cpu(sbuf[x]);
		dbuf[x] = ((pix & 0x00e00000) >> 16) |
			  ((pix & 0x0000e000) >> 11) |
			  ((pix & 0x000000c0) >> 6);
	}
}

Noralf.

> Either way, lgtm:
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
>> +			  ((sbuf[x] & 0x0000e000) >> 11) |
>> +			  ((sbuf[x] & 0x000000c0) >> 6);
>> +}
>> +
>> +/**
>> + * drm_fb_xrgb8888_to_rgb332 - Convert XRGB8888 to RGB332 clip buffer
>> + * @dst: RGB332 destination buffer
>> + * @src: XRGB8888 source buffer
>> + * @fb: DRM framebuffer
>> + * @clip: Clip rectangle area to copy
>> + *
>> + * Drivers can use this function for RGB332 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_rgb332(void *dst, void *src, struct drm_framebuffer *fb,
>> +			       struct drm_rect *clip)
>> +{
>> +	size_t width = drm_rect_width(clip);
>> +	size_t src_len = width * sizeof(u32);
>> +	unsigned int y;
>> +	void *sbuf;
>> +
>> +	/* Use a buffer to speed up access on buffers with uncached read mapping (i.e. WC) */
>> +	sbuf = kmalloc(src_len, GFP_KERNEL);
>> +	if (!sbuf)
>> +		return;
>> +
>> +	src += clip_offset(clip, fb->pitches[0], sizeof(u32));
>> +	for (y = 0; y < drm_rect_height(clip); y++) {
>> +		memcpy(sbuf, src, src_len);
>> +		drm_fb_xrgb8888_to_rgb332_line(dst, sbuf, width);
>> +		src += fb->pitches[0];
>> +		dst += width;
>> +	}
>> +
>> +	kfree(sbuf);
>> +}
>> +EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb332);
>> +
>>  static void drm_fb_xrgb8888_to_rgb565_line(u16 *dbuf, u32 *sbuf,
>>  					   unsigned int pixels,
>>  					   bool swab)
>> diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
>> index 4e0258a61311..d0809aff5cf8 100644
>> --- a/include/drm/drm_format_helper.h
>> +++ b/include/drm/drm_format_helper.h
>> @@ -16,6 +16,8 @@ void drm_fb_memcpy_dstclip(void __iomem *dst, unsigned int dst_pitch, void *vadd
>>  			   struct drm_rect *clip);
>>  void drm_fb_swab(void *dst, void *src, struct drm_framebuffer *fb,
>>  		 struct drm_rect *clip, bool cached);
>> +void drm_fb_xrgb8888_to_rgb332(void *dst, void *vaddr, struct drm_framebuffer *fb,
>> +			       struct drm_rect *clip);
>>  void drm_fb_xrgb8888_to_rgb565(void *dst, void *vaddr,
>>  			       struct drm_framebuffer *fb,
>>  			       struct drm_rect *clip, bool swab);
>> -- 
>> 2.32.0
>>
>