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Message-ID: <47100413-db63-1efa-45e9-028dfc430b7e@suse.de>
Date: Fri, 4 Feb 2022 16:52:54 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Javier Martinez Canillas <javierm@...hat.com>,
linux-kernel@...r.kernel.org
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
linux-fbdev@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
dri-devel@...ts.freedesktop.org,
Noralf Trønnes <noralf@...nnes.org>,
Maxime Ripard <maxime@...no.tech>,
Daniel Vetter <daniel@...ll.ch>,
David Airlie <airlied@...ux.ie>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>
Subject: Re: [PATCH v2 1/4] drm/format-helper: Add
drm_fb_{xrgb8888,gray8}_to_mono_reversed()
Hi
Am 04.02.22 um 14:43 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>
> ---
>
> (no changes since v1)
>
> drivers/gpu/drm/drm_format_helper.c | 80 +++++++++++++++++++++++++++++
> include/drm/drm_format_helper.h | 7 +++
> 2 files changed, 87 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index 0f28dd2bdd72..cdce4b7c25d9 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -584,3 +584,83 @@ 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, 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)
> + u8 byte = 0x00;
> +
> + for (i = 0; i < 8; i++) {
> + 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
> + * @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 *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).
> +
> + 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.
> + gray8 += dst_pitch;
'gray8 += fb->pitches[0]' would be correct.
> + }
> +}
> +
> +/**
> + * 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, ...);
src += fb->pitches[0]
dst += dst_pitch;
}
kfree(tmp);
}
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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