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@xxxxxxxxxxxxxx>
> ---
> 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
