From: Javier Martinez Canillas <javierm@redhat.com>
To: Thomas Zimmermann <tzimmermann@suse.de>, linux-kernel@vger.kernel.org
Cc: "Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Geert Uytterhoeven" <geert@linux-m68k.org>,
linux-fbdev@vger.kernel.org, "Sam Ravnborg" <sam@ravnborg.org>,
dri-devel@lists.freedesktop.org,
"Noralf Trønnes" <noralf@tronnes.org>,
"Maxime Ripard" <maxime@cerno.tech>,
"Daniel Vetter" <daniel@ffwll.ch>,
"David Airlie" <airlied@linux.ie>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Maxime Ripard" <mripard@kernel.org>
Subject: Re: [PATCH v2 1/4] drm/format-helper: Add drm_fb_{xrgb8888,gray8}_to_mono_reversed()
Date: Fri, 4 Feb 2022 20:31:36 +0100 [thread overview]
Message-ID: <b388f295-920a-b4fc-41ef-d090bdcd69e2@redhat.com> (raw)
In-Reply-To: <47100413-db63-1efa-45e9-028dfc430b7e@suse.de>
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
next prev parent reply other threads:[~2022-02-04 19:31 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-04 13:43 [PATCH v2 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays Javier Martinez Canillas
2022-02-04 13:43 ` [PATCH v2 1/4] drm/format-helper: Add drm_fb_{xrgb8888,gray8}_to_mono_reversed() Javier Martinez Canillas
2022-02-04 15:52 ` Thomas Zimmermann
2022-02-04 16:00 ` Thomas Zimmermann
2022-02-04 19:31 ` Javier Martinez Canillas [this message]
2022-02-04 20:35 ` Thomas Zimmermann
2022-02-04 21:02 ` Ilia Mirkin
2022-02-07 12:44 ` [PATCH v2 1/4] drm/format-helper: Add drm_fb_{xrgb8888, gray8}_to_mono_reversed() Thomas Zimmermann
2022-02-04 13:43 ` [PATCH v2 2/4] drm/tiny: Add driver for Solomon SSD130X OLED displays Javier Martinez Canillas
2022-02-04 14:26 ` Andy Shevchenko
2022-02-04 19:19 ` Javier Martinez Canillas
2022-02-05 13:04 ` Andy Shevchenko
2022-02-05 17:40 ` Javier Martinez Canillas
2022-02-04 13:43 ` [PATCH v2 3/4] MAINTAINERS: Add entry for Solomon SSD130X OLED displays DRM driver Javier Martinez Canillas
2022-02-04 13:57 ` Andy Shevchenko
2022-02-04 14:12 ` Javier Martinez Canillas
2022-02-04 14:28 ` Andy Shevchenko
2022-02-04 14:33 ` Javier Martinez Canillas
2022-02-04 13:43 ` [PATCH v2 4/4] dt-bindings: display: ssd1307fb: Add myself as binding co-maintainer Javier Martinez Canillas
2022-02-09 22:14 ` Rob Herring
2022-02-04 14:31 ` [PATCH v2 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays Geert Uytterhoeven
2022-02-04 14:37 ` Javier Martinez Canillas
2022-02-08 14:19 ` Geert Uytterhoeven
2022-02-08 15:10 ` Javier Martinez Canillas
2022-02-08 15:18 ` Mark Brown
2022-02-08 15:32 ` Javier Martinez Canillas
2022-02-08 15:23 ` Geert Uytterhoeven
2022-02-08 15:40 ` Javier Martinez Canillas
2022-02-08 17:19 ` Javier Martinez Canillas
2022-02-09 13:47 ` Andy Shevchenko
2022-02-09 14:27 ` Geert Uytterhoeven
2022-02-09 14:42 ` Javier Martinez Canillas
2022-02-09 15:32 ` Andy Shevchenko
2022-02-10 8:32 ` Maxime Ripard
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