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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Sam Ravnborg <sam@ravnborg.org>
Cc: David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Maxime Ripard <mripard@kernel.org>,
	Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	DRI Development <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH resend 4/5] video: fbdev: ssd1307fb: Optimize screen updates
Date: Tue, 20 Jul 2021 11:16:27 +0200	[thread overview]
Message-ID: <CAMuHMdVpxVJx8=aGasrop6soO011gby8Xxotr+Yomi9oBOTrpA@mail.gmail.com> (raw)
In-Reply-To: <CAMuHMdVyuzQzXF0X3OA=PH4E4ifaT2TfHs76yGgRKk-XrEbwzw@mail.gmail.com>

Hi Sam,

On Tue, Jul 20, 2021 at 9:56 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Mon, Jul 19, 2021 at 9:21 PM Sam Ravnborg <sam@ravnborg.org> wrote:
> > On Wed, Jul 14, 2021 at 04:58:03PM +0200, Geert Uytterhoeven wrote:
> > > Currently, each screen update triggers an I2C transfer of all screen
> > > data, up to 1 KiB of data for a 128x64 display, which takes at least 20
> > > ms in Fast mode.
> > >
> > > Reduce the amount of transferred data by only updating the rectangle
> > > that changed.  Remove the call to ssd1307fb_set_address_range() during
> > > initialization, as ssd1307fb_update_rect() now takes care of that.
> > >
> > > Note that for now the optimized operation is only used for fillrect,
> > > copyarea, and imageblit, which are used by fbcon.
> > >
> > > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
>
> > > --- a/drivers/video/fbdev/ssd1307fb.c
> > > +++ b/drivers/video/fbdev/ssd1307fb.c
> > > @@ -184,16 +184,18 @@ static int ssd1307fb_set_address_range(struct ssd1307fb_par *par, u8 col_start,
> > >       return ssd1307fb_write_cmd(par->client, page_end);
> > >  }
> > >
> > > -static int ssd1307fb_update_display(struct ssd1307fb_par *par)
> > > +static int ssd1307fb_update_rect(struct ssd1307fb_par *par, unsigned int x,
> > > +                              unsigned int y, unsigned int width,
> > > +                              unsigned int height)
> > >  {
> > >       struct ssd1307fb_array *array;
> > >       u8 *vmem = par->info->screen_buffer;
> > >       unsigned int line_length = par->info->fix.line_length;
> > > -     unsigned int pages = DIV_ROUND_UP(par->height, 8);
> > > +     unsigned int pages = DIV_ROUND_UP(height + y % 8, 8);
> >
> > Add () like this - at least it helps me:
> > > +     unsigned int pages = DIV_ROUND_UP((height + y) % 8, 8);
>
> Thanks, that's actually a genuine bug.

No it's not "(height + y) % 8" is wrong.

Better if I reorder the operands like below?

    unsigned int pages = DIV_ROUND_UP(y % 8 + height, 8);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

  reply	other threads:[~2021-07-20  9:17 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14 14:57 [PATCH resend 0/5] video: fbdev: ssd1307fb: Optimizations and improvements Geert Uytterhoeven
2021-07-14 14:58 ` [PATCH resend 1/5] video: fbdev: ssd1307fb: Propagate errors via ssd1307fb_update_display() Geert Uytterhoeven
2021-07-14 14:58 ` [PATCH resend 2/5] video: fbdev: ssd1307fb: Simplify ssd1307fb_update_display() Geert Uytterhoeven
     [not found]   ` <YPXM8AXNje7GXf+i@ravnborg.org>
2021-07-20  7:43     ` Geert Uytterhoeven
2021-07-14 14:58 ` [PATCH resend 3/5] video: fbdev: ssd1307fb: Extract ssd1307fb_set_address_range() Geert Uytterhoeven
     [not found]   ` <YPXNdJNpYoPSpxSb@ravnborg.org>
2021-07-20  7:51     ` Geert Uytterhoeven
2021-07-14 14:58 ` [PATCH resend 4/5] video: fbdev: ssd1307fb: Optimize screen updates Geert Uytterhoeven
     [not found]   ` <YPXQnlpWUa1QaZKd@ravnborg.org>
2021-07-20  7:56     ` Geert Uytterhoeven
2021-07-20  9:16       ` Geert Uytterhoeven [this message]
2021-07-14 14:58 ` [PATCH resend 5/5] video: fbdev: ssd1307fb: Cache address ranges Geert Uytterhoeven
     [not found] ` <YO8CT+Hcw1wfhnH5@ravnborg.org>
2021-07-15  6:54   ` [PATCH resend 0/5] video: fbdev: ssd1307fb: Optimizations and improvements Geert Uytterhoeven
2021-07-20 14:53     ` Daniel Vetter
     [not found] ` <YPXRMXQxCW+Agaz8@ravnborg.org>
2021-07-20  7:33   ` Geert Uytterhoeven

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