Date:   Wed, 9 Feb 2022 13:51:34 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-fbdev@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Noralf Trønnes <noralf@...nnes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <maxime@...no.tech>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v3 2/7] drm/format-helper: Add drm_fb_{xrgb8888,
 gray8}_to_mono_reversed()

Hi

Am 09.02.22 um 10:03 schrieb Javier Martinez Canillas:
> Add support to convert XR24 and 8-bit grayscale to reversed monochrome for
> drivers that control monochromatic panels, that only have 1 bit per pixel.
> 
> The drm_fb_gray8_to_mono_reversed() helper was based on the function that
> does the same in the drivers/gpu/drm/tiny/repaper.c driver.
> 
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
> 
> Changes in v3:
> - Also add a drm_fb_xrgb8888_to_mono_reversed() helper (Thomas Zimmermann)
> - Split lines copy to drm_fb_gray8_to_mono_reversed_line() (Thomas Zimmermann)
> - Handle case where the source buffer is not aligned to 8 (Thomas Zimmermann)
> 
>   drivers/gpu/drm/drm_format_helper.c | 157 ++++++++++++++++++++++++++++
>   include/drm/drm_format_helper.h     |   8 ++
>   2 files changed, 165 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index b981712623d3..19710342c0de 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -591,3 +591,160 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
>   	return -EINVAL;
>   }
>   EXPORT_SYMBOL(drm_fb_blit_toio);
> +
> +static void drm_fb_gray8_to_mono_reversed_line(u8 *dst, const u8 *src, unsigned int pixels,
> +					       unsigned int start_offset, unsigned int end_offset)
> +{
> +	unsigned int xb, i;
> +
> +	for (xb = 0; xb < pixels; xb++) {
> +		unsigned int start = 0, end = 8;
> +		u8 byte = 0x00;
> +
> +		if (xb == 0 && start_offset)
> +			start = start_offset;
> +
> +		if (xb == pixels - 1 && end_offset)
> +			end = end_offset;

end_offset should be called end_len, because it is the number of bits in
the final byte; but not the offset of the final bit.

> +
> +		for (i = start; i < end; i++) {
> +			unsigned int x = xb * 8 + i;
> +
> +			byte >>= 1;
> +			if (src[x] >> 7)
> +				byte |= BIT(7);
> +		}
> +		*dst++ = byte;
> +	}
> +}
> +
> +/**
> + * drm_fb_gray8_to_mono_reversed - Convert grayscale to reversed monochrome
> + * @dst: reversed monochrome destination buffer
> + * @dst_pitch: Number of bytes between two consecutive scanlines within dst
> + * @src: 8-bit grayscale 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 drm_fb_xrgb8888_to_gray8() to convert to grayscale and then this
> + * helper function to convert to the native format.
> + */
> +void drm_fb_gray8_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *vaddr,
> +				   const struct drm_framebuffer *fb,
> +				   const struct drm_rect *clip)
> +{
> +
> +	unsigned int linepixels = drm_rect_width(clip);
> +	unsigned int lines = drm_rect_height(clip);
> +	unsigned int start_offset, end_offset;
> +	unsigned int y;
> +	const u8 *gray8 = vaddr;
> +	u8 *mono = dst;
> +
> +	/*
> +	 * The reversed mono destination buffer contains 1 bit per pixel
> +	 * and destination scanlines have to be in multiple of 8 pixels.
> +	 */
> +	if (!dst_pitch)
> +		dst_pitch = DIV_ROUND_UP(linepixels, 8);
> +
> +	/*
> +	 * For damage handling, it is possible that only parts of the source
> +	 * buffer is copied and this could lead to start and end pixels that
> +	 * are not aligned to multiple of 8.
> +	 *
> +	 * Calculate if the start and end pixels are not aligned and set the
> +	 * offsets for the reversed mono line conversion function to adjust.
> +	 */
> +	start_offset = clip->x1 % 8;
> +	end_offset = clip->x2 % 8;
> +
> +	for (y = 0; y < lines; y++) {
> +		drm_fb_gray8_to_mono_reversed_line(mono, gray8, dst_pitch,
> +						   start_offset, end_offset);
> +		gray8 += fb->pitches[0];
> +		mono += dst_pitch;
> +	}
> +}

Do you really need that function. It's not exported and if it's not 
otherwise used, I'd just remove it.  We don't keep unused interfaces around.

> +
> +/**
> + * drm_fb_xrgb8888_to_mono_reversed - Convert XRGB8888 to reversed monochrome
> + * @dst: reversed monochrome destination buffer
> + * @dst_pitch: Number of bytes between two consecutive scanlines within dst
> + * @src: XRGB8888 source buffer
> + * @fb: DRM framebuffer
> + * @clip: Clip rectangle area to copy
> + *
> + * DRM doesn't have native monochrome support.
> + * Such drivers can announce the commonly supported XR24 format to userspace
> + * and use this function to convert to the native format.
> + *
> + * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
> + * then the result is converted from grayscale to reversed monohrome.
> + */
> +void drm_fb_xrgb8888_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *vaddr,
> +				      const struct drm_framebuffer *fb, const struct drm_rect *clip)
> +{
> +	unsigned int linepixels = drm_rect_width(clip);
> +	unsigned int lines = clip->y2 - clip->y1;
> +	unsigned int cpp = fb->format->cpp[0];
> +	unsigned int len_src32 = linepixels * cpp;
> +	unsigned int start_offset, end_offset;
> +	unsigned int y;
> +	u8 *mono = dst, *gray8;
> +	u32 *src32;
> +
> +	if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
> +		return;
> +
> +	/*
> +	 * The reversed mono destination buffer contains 1 bit per pixel
> +	 * and destination scanlines have to be in multiple of 8 pixels.
> +	 */
> +	if (!dst_pitch)
> +		dst_pitch = DIV_ROUND_UP(linepixels, 8);

I'd do a warn_once if (dst_pitch % 8 != 0).


> +
> +	/*
> +	 * The cma memory is write-combined so reads are uncached.
> +	 * Speed up by fetching one line at a time.

I once had a patchset that adds caching information to struct 
dma_buf_map (soon to be named struct iosys_map).  Blitting helpers would 
be able to enable/disable this optimization as needed.

However, your driver doesn't use CMA. It's backed by SHMEM. Do you 
really want to keep that code in?


> +	 */
> +	src32 = kmalloc(len_src32, GFP_KERNEL);
> +	if (!src32)
> +		return;
> +
> +	/*
> +	 * Copies are done line-by-line, allocate an intermediate
> +	 * buffer to copy the gray8 lines and then convert to mono.
> +	 */
> +	gray8 = kmalloc(linepixels, GFP_KERNEL);
> +	if (!gray8)
> +		goto free_src32;

If might be faster to allocate both buffers in one step and set the 
pointers into the allocated buffer.

> +
> +	/*
> +	 * For damage handling, it is possible that only parts of the source
> +	 * buffer is copied and this could lead to start and end pixels that
> +	 * are not aligned to multiple of 8.
> +	 *
> +	 * Calculate if the start and end pixels are not aligned and set the
> +	 * offsets for the reversed mono line conversion function to adjust.
> +	 */
> +	start_offset = clip->x1 % 8;
> +	end_offset = clip->x2 % 8;

end_len, again. If you have 1 single bit set in the final byte, the
offset is 0, but the length is 1.

Best regards
Thomas

> +
> +	vaddr += clip_offset(clip, fb->pitches[0], cpp);
> +	for (y = 0; y < lines; y++) {
> +		src32 = memcpy(src32, vaddr, len_src32);
> +		drm_fb_xrgb8888_to_gray8_line(gray8, src32, linepixels);
> +		drm_fb_gray8_to_mono_reversed_line(mono, gray8, dst_pitch,
> +						   start_offset, end_offset);
> +		vaddr += fb->pitches[0];
> +		mono += dst_pitch;
> +	}
> +
> +	kfree(gray8);
> +free_src32:
> +	kfree(src32);
> +}
> +EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono_reversed);
> diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
> index b30ed5de0a33..6638da9e9774 100644
> --- a/include/drm/drm_format_helper.h
> +++ b/include/drm/drm_format_helper.h
> @@ -43,4 +43,12 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
>   		     const void *vmap, const struct drm_framebuffer *fb,
>   		     const struct drm_rect *rect);
>   
> +void drm_fb_gray8_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *src,
> +				   const struct drm_framebuffer *fb,
> +				   const struct drm_rect *clip);
> +
> +void drm_fb_xrgb8888_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *src,
> +				      const struct drm_framebuffer *fb,
> +				      const struct drm_rect *clip);
> +
>   #endif /* __LINUX_DRM_FORMAT_HELPER_H */

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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