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