[PATCH 2/4] drm/format-helper: Add drm_fb_gray8_to_mono_reversed()

[Thomas Zimmermann]

Hi

Am 31.01.22 um 21:12 schrieb Javier Martinez Canillas:
> Add support to convert 8-bit grayscale to reversed monochrome for drivers
> that control monochromatic displays, that only have 1 bit per pixel depth.
> 
> This helper function was based on repaper_gray8_to_mono_reversed() from
> the drivers/gpu/drm/tiny/repaper.c driver.

You could convert repaper to the new helper.

> 
> Signed-off-by: Javier Martinez Canillas <javierm at redhat.com>
> ---
> 
>   drivers/gpu/drm/drm_format_helper.c | 35 +++++++++++++++++++++++++++++
>   include/drm/drm_format_helper.h     |  2 ++
>   2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index 0f28dd2bdd72..bf477c136082 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -584,3 +584,38 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
>   	return -EINVAL;
>   }
>   EXPORT_SYMBOL(drm_fb_blit_toio);
> +
> +/**
> + * drm_fb_gray8_to_mono_reversed - Convert grayscale to reversed monochrome
> + * @dst: reversed monochrome destination buffer
> + * @src: 8-bit grayscale source buffer
> + * @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, void *src, const struct drm_rect *clip)

IMHO it would be better to have a function that converts xrgb8888 to 
mono and let it handle the intermediate step of gray8.

> +{
> +	size_t width = drm_rect_width(clip);
> +	size_t height = drm_rect_width(clip);
> +
> +	u8 *mono = dst, *gray8 = src;
> +	unsigned int y, xb, i;
> +
> +	for (y = 0; y < height; y++)
> +		for (xb = 0; xb < width / 8; xb++) {

The inner loop should probably go into a separate helper function. See 
the drm_fb_*_line() helpers in this file

At some point, we's want to have a single blit helper that takes source 
and destination formats/buffers. It would then pick the correct per-line 
helper for the conversion. So yeah, we'd want something composable.

Best regards
Thomas

> +			u8 byte = 0x00;
> +
> +			for (i = 0; i < 8; i++) {
> +				int x = xb * 8 + i;
> +
> +				byte >>= 1;
> +				if (gray8[y * width + x] >> 7)
> +					byte |= BIT(7);
> +			}
> +			*mono++ = byte;
> +		}
> +}
> +EXPORT_SYMBOL(drm_fb_gray8_to_mono_reversed);
> diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
> index b30ed5de0a33..cd4c8b7c78de 100644
> --- a/include/drm/drm_format_helper.h
> +++ b/include/drm/drm_format_helper.h
> @@ -43,4 +43,6 @@ 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, void *vaddr, 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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