linux-kernel - Re: [PATCH v2 1/4] drm/format-helper: Add drm_fb_{xrgb8888,gray8}_to_mono

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Date:   Fri, 4 Feb 2022 16:02:08 -0500
From:   Ilia Mirkin <imirkin@...m.mit.edu>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fbdev <linux-fbdev@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <maxime@...no.tech>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v2 1/4] drm/format-helper: Add drm_fb_{xrgb8888,gray8}_to_mono_reversed()

On Fri, Feb 4, 2022 at 10:53 AM Thomas Zimmermann <tzimmermann@...e.de> wrote:
>
> 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)

Not sure if it's relevant, but 1366x768 was a fairly popular laptop
resolution. There's even a dedicated drm_mode_fixup_1366x768 in
drm_edid.c. (Would it have killed them to add 2 more horizontal
pixels? Apparently.)

Cheers,

  -ilia