Re: [PATCH resend 2/5] video: fbdev: ssd1307fb: Simplify ssd1307fb_update_display()

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