Hi Sam,
On Mon, Jul 19, 2021 at 9:05 PM Sam Ravnborg sam@ravnborg.org wrote:
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:
- Move last page handling one level up, as the value of "m" is the same inside a page,
- 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?
"the loop" is the j-loop? If m is less than 8 for the last page, it should be less than 8 for all iterations of j, as all last bytes in each "line" (visible row) are partial, cfr. the comments above the code, explaining the representation of the screen.
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; } }
Gr{oetje,eeting}s,
Geert