[Qemu-devel] [PULL 3/8] ati-vga: Fix GPIO_MONID register write

[Gerd Hoffmann <kraxel@redhat.com>]

From: BALATON Zoltan <balaton@eik.bme.hu>

Also update bitbang_i2c state when output bits are changed while
enable bits are set. This fixes EDID access by the ATI FCode ROM.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-id: 292e70a92b7fbfd9a4120d433dbdcfda4e5f6c3c.1565558093.git.balaton@eik.bme.hu
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/display/ati.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/hw/display/ati.c b/hw/display/ati.c
index 6cdcbef238fe..eb54f6842fed 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -564,12 +564,15 @@ static void ati_mm_write(void *opaque, hwaddr addr,
                                addr - GPIO_MONID, data, size);
             /*
              * Rage128p accesses DDC used to get EDID via these bits.
-             * Only touch i2c when write overlaps 3rd byte because some
-             * drivers access this reg via multiple partial writes and
-             * without this spurious bits would be sent.
+             * Because some drivers access this via multiple byte writes
+             * we have to be careful when we send bits to avoid spurious
+             * changes in bitbang_i2c state. So only do it when mask is set
+             * and either the enable bits are changed or output bits changed
+             * while enabled.
              */
             if ((s->regs.gpio_monid & BIT(25)) &&
-                addr <= GPIO_MONID + 2 && addr + size > GPIO_MONID + 2) {
+                ((addr <= GPIO_MONID + 2 && addr + size > GPIO_MONID + 2) ||
+                 (addr == GPIO_MONID && (s->regs.gpio_monid & 0x60000)))) {
                 s->regs.gpio_monid = ati_i2c(&s->bbi2c, s->regs.gpio_monid, 1);
             }
         }
-- 
2.18.1