[PATCH resend 4/5] video: fbdev: ssd1307fb: Optimize screen updates

Geert Uytterhoeven
2021-07-14T14:58:16Z

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>
---
drivers/video/fbdev/ssd1307fb.c | 43 ++++++++++++++++++++-------------
1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/drivers/video/fbdev/ssd1307fb.c b/drivers/video/fbdev/ssd1307fb.c
index cfa27ea0feab4f01..8e3d4be74723b9bf 100644
--- 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);
u32 array_idx = 0;
int ret, i, j, k;

- array = ssd1307fb_alloc_array(par->width * pages, SSD1307FB_DATA);
+ array = ssd1307fb_alloc_array(width * pages, SSD1307FB_DATA);
if (!array)
return -ENOMEM;

@@ -226,13 +228,18 @@ static int ssd1307fb_update_display(struct ssd1307fb_par *par)
* (5) A4 B4 C4 D4 E4 F4 G4 H4
*/

- for (i = 0; i < pages; i++) {
+ ret = ssd1307fb_set_address_range(par, par->col_offset + x, width,
+ par->page_offset + y / 8, pages);
+ if (ret < 0)
+ goto out_free;
+
+ for (i = y / 8; i < y / 8 + pages; i++) {
int m = 8;

/* Last page may be partial */
- if (i + 1 == pages && par->height % 8)
+ if (8 * (i + 1) > par->height)
m = par->height % 8;
- for (j = 0; j < par->width; j++) {
+ for (j = x; j < x + width; j++) {
u8 data = 0;

for (k = 0; k < m; k++) {
@@ -245,11 +252,17 @@ static int ssd1307fb_update_display(struct ssd1307fb_par *par)
}
}

- ret = ssd1307fb_write_array(par->client, array, par->width * pages);
+ ret = ssd1307fb_write_array(par->client, array, width * pages);
+
+out_free:
kfree(array);
return ret;
}

+static int ssd1307fb_update_display(struct ssd1307fb_par *par)
+{
+ return ssd1307fb_update_rect(par, 0, 0, par->width, par->height);
+}

static ssize_t ssd1307fb_write(struct fb_info *info, const char __user *buf,
size_t count, loff_t *ppos)
@@ -299,21 +312,24 @@ static void ssd1307fb_fillrect(struct fb_info *info, const struct fb_fillrect *r
{
struct ssd1307fb_par *par = info->par;
sys_fillrect(info, rect);
- ssd1307fb_update_display(par);
+ ssd1307fb_update_rect(par, rect->dx, rect->dy, rect->width,
+ rect->height);
}

static void ssd1307fb_copyarea(struct fb_info *info, const struct fb_copyarea *area)
{
struct ssd1307fb_par *par = info->par;
sys_copyarea(info, area);
- ssd1307fb_update_display(par);
+ ssd1307fb_update_rect(par, area->dx, area->dy, area->width,
+ area->height);
}

static void ssd1307fb_imageblit(struct fb_info *info, const struct fb_image *image)
{
struct ssd1307fb_par *par = info->par;
sys_imageblit(info, image);
- ssd1307fb_update_display(par);
+ ssd1307fb_update_rect(par, image->dx, image->dy, image->width,
+ image->height);
}

static const struct fb_ops ssd1307fb_ops = {
@@ -493,13 +509,6 @@ static int ssd1307fb_init(struct ssd1307fb_par *par)
if (ret < 0)
return ret;

- /* Set column and page range */
- ret = ssd1307fb_set_address_range(par, par->col_offset, par->width,
- par->page_offset,
- DIV_ROUND_UP(par->height, 8));
- if (ret < 0)
- return ret;
-
/* Clear the screen */
ret = ssd1307fb_update_display(par);
if (ret < 0)
--
2.25.1