| Message ID | 20210714145804.2530727-3-geert@linux-m68k.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | video: fbdev: ssd1307fb: Optimizations and improvements | expand |
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
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: > > 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? "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
Hi Geert, On Tue, Jul 20, 2021 at 09:43:22AM +0200, Geert Uytterhoeven wrote: > 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: > > > 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? > > "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. OK, then the code works as intended. I had not read the comments and just assume it was only the last byte that was in need of a special treatment. So code is fine: Acked-by: Sam Ravnborg <sam@ravnborg.org> > > > > 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 > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds
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++) { 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; } }
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(-)