Geert Uytterhoeven wrote: > This depends on which of these two is fastest for scrolling the console: > - panning the virtual screen and redrawing the missing part: set > FBINFO_PARTIAL_PAN_OK > - copying or redrawing the screen: don't set FBINFO_PARTIAL_PAN_OK I'm a little confused about panning support in my driver (which I didn't write -- I'm just cleaning it up). There is .fb_pan_display function, but it only gets called early in the boot process, and only with xoffset=0 and yoffset=0. After that, it never seems to get called again. Under what circumstances is panning really used? > >> I have the same problem with FBINFO_READS_FAST. > > You should set this flag if reading from frame buffer memory is a fast > operation. > On many graphics devices, reading from frame buffer memory is much slower > than writing. As you use system RAM, you probably want to set it. I see a lot of drivers that set FBINFO_VIRTFB but don't set FBINFO_READS_FAST. Why? > If this flag is set, scrolling is implemented by copying memory around. > If not set, scrolling is implemented by redrawing the whole screen. > > A simple way to find the optimal settings of both flags (all 4 combinations) is > running "clear; time cat big_text_file" and comparing the timing results That's the funny thing -- I've been trying various combinations of FBINFO_VIRTFB, FBINFO_PARTIAL_PAN_OK, and FBINFO_READS_FAST, and I always get the same timing result. It seems to have no affect on performance. -- Timur Tabi Linux kernel developer at Freescale -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
