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

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Aug 30, 2021 at 02:08:14PM +0200, Noralf Trønnes wrote:
> 
> 
> 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@suse.de>
> >> Signed-off-by: Noralf Trønnes <noralf@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.

Essentially add half of the lowest bit before you mask, so

((sbuf[x] + 0x10) & 0xe0 )

I dropped the shift to make it clear what's going on. If you're mask is
0xc0, then you simply add 0x20 before masking.

> > 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()?

I think so.

Plus on any format that has u16 output we'd need a cpu_to_le16 wrapped
around the entire thing.
-Daniel

> 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@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
> >>
> > 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch