It is common practice when implementing double-buffering
on VideoCore to do so by multiplying the height of the
virtual buffer by the number of virtual screens desired
(i.e., two - in the case of double-bufferring).
At present, this won't work in QEMU because the logic in
fb_use_offsets require that both the virtual width and
height exceed their physical counterparts.
This appears to be unintentional/a typo and indeed the
comment states; "Experimentally, the hardware seems to
do this only if the viewport size is larger than the
physical screen". The viewport/virtual size would be
larger than the physical size if either virtual dimension
were larger than their physical counterparts and not
necessarily both.
Signed-off-by: SamJakob <m...@samjakob.com>
---
hw/display/bcm2835_fb.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/hw/display/bcm2835_fb.c b/hw/display/bcm2835_fb.c
index e40ed2d2e1..650db3da82 100644
--- a/hw/display/bcm2835_fb.c
+++ b/hw/display/bcm2835_fb.c
@@ -145,7 +145,7 @@ static bool fb_use_offsets(BCM2835FBConfig *config)
* viewport size is larger than the physical screen. (It doesn't
* prevent the guest setting this silly viewport setting, though...)
*/
- return config->xres_virtual > config->xres &&
+ return config->xres_virtual > config->xres ||
config->yres_virtual > config->yres;
}
--
2.45.2
