@@ -213,8 +213,18 @@ psplash_fb_new (int angle, int fbdev_id)
perror(" Error getting the fixed framebuffer info");
goto fail;
} else {
- DBG("Virtual resolution set to double");
- fb->double_buffering = 1;
+ if (ioctl(fb->fd, FBIOPAN_DISPLAY, &fb_var) == -1) {
+ fprintf(stderr, "warning: FBIOPAN_DISPLAY failed, "
+ "double buffering disabled\n");
+ } else {
+ if (fb_var.yres_virtual == fb_var.yres * 2) {
+ DBG("Virtual resolution set to double");
+ fb->double_buffering = 1;
+ } else {
+ fprintf(stderr, "warning: Doubling virtual "
+ "resolution failed, double buffering disabled\n");
+ }
+ }
}
}
}
Some fb drivers do not implement double buffering completely or correctly. For example mxsfb driver does not set yres_virtual to double on initialization, nor it allows its doubling by FBIOPUT_VSCREENINFO ioctl call. In such case, the double buffering gets enabled, but psplash fails to display every second frame with error 'psplash_fb_flip: FBIOPAN_DISPLAY failed: Invalid argument'. Panning the display by FBIOPAN_DISPLAY ioctl is always checking carefully that the resolution, virtual buffer resolutin and offsets are in bounds at fb_pan_display - https://elixir.bootlin.com/linux/v4.9.275/source/drivers/video/fbdev/core/fbmem.c#L891. Swapping the front and back buffers is done by switching the yoffset between 0 and yres values. For double buffering, the whole buffer must have yres_virtual buffer size double of yres. But in case of the mxsfb driver, the yres_virtual is always equal to yres, so drawing with the offset set to yres would overrun the buffer. So the panning is stopped and error 'Invalid argument' is returned. Psplash tries to double the yres_virtual on initialization by FBIOPUT_VSCREENINFO ioctl call, that at some point calls the mxsfb_check_var - https://elixir.bootlin.com/linux/v4.9.275/source/drivers/video/fbdev/mxsfb.c#L269 function, which for some reason always sets the yres_virtual back to yres, effectively canceling the doubling. But no error is returned in this case, so it gets silently ignored. So in general, checking for the ioctl call success is not enough as some drivers may pass this test, but fail double buffering anyway. So now we double check the yres_virtual on fb_new and disable double buffering in case of doubling yres_virtual fails. Signed-off-by: Michal Horn <michalhorn@eaton.com> --- psplash-fb.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) -- 2.25.1