| Message ID | 20240713155656.59431-1-me@samjakob.com |
|---|---|
| State | New |
| Headers | show |
| Series | hw/display/bcm2835_fb: fix fb_use_offsets condition | expand |
On 13/7/24 17:56, SamJakob wrote: > 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 <me@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; > } > Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
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; }
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 <me@samjakob.com> --- hw/display/bcm2835_fb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)