From 1d3ea28fd7da9a23e278be70c7e028fbd2b69bf3 Mon Sep 17 00:00:00 2001
From: qihao <qihao_yewu@cmss.chinamobile.com>
Date: Thu, 25 Jul 2024 10:29:20 +0800
Subject: [PATCH] hw/display/bcm2835_fb: fix fb_use_offsets condition
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cheery-pick from 345acc443905eda8008a1d328dd89b73c4a3f89e

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>
Message-id: 20240713160353.62410-1-me@samjakob.com
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: qihao_yewu <qihao_yewu@cmss.chinamobile.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 a05277674f..c45da149d9 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;
 }
 
-- 
2.41.0.windows.1