From: Sam Ravnborg <sam@ravnborg.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-fbdev@vger.kernel.org, David Airlie <airlied@linux.ie>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH resend 2/5] video: fbdev: ssd1307fb: Simplify ssd1307fb_update_display()
Date: Mon, 19 Jul 2021 21:05:20 +0200 [thread overview]
Message-ID: <YPXM8AXNje7GXf+i@ravnborg.org> (raw)
In-Reply-To: <20210714145804.2530727-3-geert@linux-m68k.org>
Hi Geert,
On Wed, Jul 14, 2021 at 04:58:01PM +0200, Geert Uytterhoeven wrote:
> Simplify the nested loops to handle conversion from linear frame buffer
> to ssd1307 page layout:
> 1. Move last page handling one level up, as the value of "m" is the
> same inside a page,
> 2. array->data[] is filled linearly, so there is no need to
> recalculate array_idx over and over again; a simple increment is
> sufficient.
>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> drivers/video/fbdev/ssd1307fb.c | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/video/fbdev/ssd1307fb.c b/drivers/video/fbdev/ssd1307fb.c
> index e6b6263e3bef847f..6d7bd025bca1a175 100644
> --- a/drivers/video/fbdev/ssd1307fb.c
> +++ b/drivers/video/fbdev/ssd1307fb.c
> @@ -158,6 +158,7 @@ static int ssd1307fb_update_display(struct ssd1307fb_par *par)
> u8 *vmem = par->info->screen_buffer;
> unsigned int line_length = par->info->fix.line_length;
> unsigned int pages = DIV_ROUND_UP(par->height, 8);
> + u32 array_idx = 0;
> int ret, i, j, k;
>
> array = ssd1307fb_alloc_array(par->width * pages, SSD1307FB_DATA);
> @@ -194,19 +195,21 @@ static int ssd1307fb_update_display(struct ssd1307fb_par *par)
> */
>
> for (i = 0; i < pages; i++) {
> + int m = 8;
> +
> + /* Last page may be partial */
> + if (i + 1 == pages && par->height % 8)
> + m = par->height % 8;
> for (j = 0; j < par->width; j++) {
> - int m = 8;
> - u32 array_idx = i * par->width + j;
> - array->data[array_idx] = 0;
> - /* Last page may be partial */
> - if (i + 1 == pages && par->height % 8)
> - m = par->height % 8;
> + u8 data = 0;
> +
> for (k = 0; k < m; k++) {
If the last page is partial then m will be less than 8 for all bytes in
j = 0..par-width - but m should only be less than 8 for the last
iteration of the loop.
Do I miss something or is the code buggy?
> u8 byte = vmem[(8 * i + k) * line_length +
> j / 8];
> u8 bit = (byte >> (j % 8)) & 1;
> - array->data[array_idx] |= bit << k;
> + data |= bit << k;
> }
> + array->data[array_idx++] = data;
> }
> }
Sam
next prev parent reply other threads:[~2021-07-19 19:05 UTC|newest]
Thread overview: 21+ 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
2021-07-19 19:05 ` Sam Ravnborg [this message]
2021-07-20 7:43 ` Geert Uytterhoeven
2021-07-20 14:41 ` Sam Ravnborg
2021-07-14 14:58 ` [PATCH resend 3/5] video: fbdev: ssd1307fb: Extract ssd1307fb_set_address_range() Geert Uytterhoeven
2021-07-19 19:07 ` Sam Ravnborg
2021-07-20 7:51 ` Geert Uytterhoeven
2021-07-14 14:58 ` [PATCH resend 4/5] video: fbdev: ssd1307fb: Optimize screen updates Geert Uytterhoeven
2021-07-19 19:21 ` Sam Ravnborg
2021-07-20 7:56 ` Geert Uytterhoeven
2021-07-20 9:16 ` Geert Uytterhoeven
2021-07-20 14:39 ` Sam Ravnborg
2021-07-14 14:58 ` [PATCH resend 5/5] video: fbdev: ssd1307fb: Cache address ranges Geert Uytterhoeven
2021-07-14 15:27 ` [PATCH resend 0/5] video: fbdev: ssd1307fb: Optimizations and improvements Sam Ravnborg
2021-07-15 6:54 ` Geert Uytterhoeven
2021-07-20 14:53 ` Daniel Vetter
2021-07-19 19:23 ` Sam Ravnborg
2021-07-20 7:33 ` Geert Uytterhoeven
2021-07-20 14:45 ` Sam Ravnborg
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