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SubjectRe: [PATCH v2 1/4] drm/format-helper: Add drm_fb_{xrgb8888,gray8}_to_mono_reversed()
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Am 04.02.22 um 16:52 schrieb Thomas Zimmermann:
[...]
>> +/**
>> + * 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 *src,
>> +                      const struct drm_framebuffer *fb,
>> +                      const struct drm_rect *clip)
>> +{
>> +    if (WARN_ON(fb->format->format != DRM_FORMAT_XRGB8888))
>> +        return;
>> +
>> +    if (!dst_pitch)
>> +        dst_pitch = drm_rect_width(clip);
>> +
>> +    drm_fb_xrgb8888_to_gray8(dst, dst_pitch, src, fb, clip);
>> +    drm_fb_gray8_to_mono_reversed(dst, dst_pitch, dst, fb, clip);
>
> Converting from dst into dst can give incorrect results. At some point
> we probably want to add restrict qualifiers to these pointers, to help
> the compiler with optimizing.
>
> A better approach here is to pull the per-line conversion from
> drm_fb_xrgb8888_to_gray8() into a separate helper and implement a
> line-by-line conversion here. something like this:
>
>   drm_fb_xrgb8888_to_mono_reversed()
>   {
>     char *tmp = kmalloc(size of a single line of gray8)
>
>     for (heigth) {
>        drm_fb_xrgb8888_to_gray8_line(tmp, ..., src, ...);
>        drm_fb_gray8_to_mono_reversed(dst, ..., tmp, ...);

Here, I meant 'drm_fb_gray8_to_mono_reversed_line()'

>
>        src += fb->pitches[0]
>        dst += dst_pitch;
>     }
>
>     kfree(tmp);
>   }

To elaborate, this is an example of what I meant by composable. In the
future, we can generalize this function and hand-in 2 function pointers
the do the conversion with tmp as intermediate buffer. That would work
for any combination of formats that have a common intermediate format.

>
> Best regards
> Thomas
>
>> +}
>> +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..85e551a5cbe6 100644
>> --- a/include/drm/drm_format_helper.h
>> +++ b/include/drm/drm_format_helper.h
>> @@ -43,4 +43,11 @@ 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_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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