Hello Thomas,
Thanks a lot for your feedback.
On 2/4/22 16:52, Thomas Zimmermann wrote:
[snip]
>> +static void drm_fb_gray8_to_mono_reversed_line(u8 *dst, const u8 *src, size_t pixels)
>> +{
>> + unsigned int xb, i;
>> +
>> + for (xb = 0; xb < pixels / 8; xb++) {
>
> In practice, all mode widths are multiples of 8 because VGA mandated it.
> So it's ok-ish to assume this here. You should probably at least print a
> warning somewhere if (pixels % 8 != 0)
>
Agreed.
[snip]
>> + * 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 *src,
>> + const struct drm_rect *clip)
>
> There's a bug here. You want to pass in a drm_framebuffer as fourth
> argument.
>
>> +{
>> +
>> + size_t height = drm_rect_height(clip);
>> + size_t width = drm_rect_width(clip);
>> + unsigned int y;
>> + const u8 *gray8 = src;
>> + u8 *mono = dst;
>> +
>> + if (!dst_pitch)
>> + dst_pitch = width;
>
> The dst_pitch is given in bytes. You have to device by 8. Here would be
> a good place to warn if (width % 8 != 0).
>
Ok.
>> +
>> + for (y = 0; y < height; y++) {
>> + drm_fb_gray8_to_mono_reversed_line(mono, gray8, dst_pitch);
>> + mono += (dst_pitch / 8);
>
> The dst_pitch is already given in bytes.
>
Yes, I know but for reversed mono we want only 1/8 of the width since we
are converting from 8 bits per pixel greyscale to 1 bit per pixel mono.
Or am I misunderstanding what you meant ?
>> + gray8 += dst_pitch;
>
> 'gray8 += fb->pitches[0]' would be correct.
>
Ok.
[snip]
>> + */
>> +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, ...);
>
> src += fb->pitches[0]
> dst += dst_pitch;
> }
>
> kfree(tmp);
> }
>
I see. Yes, that sounds a much better approach. I'll change it in v3.
Best regards,
--
Javier Martinez Canillas
Linux Engineering
Red Hat
