[0/5] video: fbdev: ssd1307fb: Optimizations and improvements

Message

Geert Uytterhoeven May 18, 2021, 8:28 a.m. UTC

Hi all,

This patch series optimizes console operations on ssd1307fb, after the
customary fixes and cleanups.

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.  While many displays are smaller, and thus require less
data to be transferred, 20 ms is still an optimistic value, as the
actual data transfer may be much slower, especially on bitbanged I2C
drivers.  After this series, the amount of data transfer is reduced, as
fillrect, copyarea, and imageblit only update the rectangle that
changed.

This has been tested on an Adafruit FeatherWing OLED with an SSD1306
controller and a 128x32 OLED, connected to an OrangeCrab ECP5 FPGA board
running a 64 MHz VexRiscv RISC-V softcore, where it reduced the CPU
usage for blinking the cursor from more than 70% to ca. 10%.

Thanks for your comments!

Geert Uytterhoeven (5):
  video: fbdev: ssd1307fb: Propagate errors via
    ssd1307fb_update_display()
  video: fbdev: ssd1307fb: Simplify ssd1307fb_update_display()
  video: fbdev: ssd1307fb: Extract ssd1307fb_set_address_range()
  video: fbdev: ssd1307fb: Optimize screen updates
  video: fbdev: ssd1307fb: Cache address ranges

 drivers/video/fbdev/ssd1307fb.c | 143 +++++++++++++++++++++-----------
 1 file changed, 96 insertions(+), 47 deletions(-)