From afa0df283554d74621293851991bfedf686539a5 Mon Sep 17 00:00:00 2001
From: Jocelyn Falempe <jfalempe@redhat.com>
Date: Wed, 19 Jan 2022 11:29:05 +0100
Subject: mgag200 fix memmapsl configuration in GCTL6 register
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Git-commit: 028a73e10705af1ffd51f2537460f616dc58680e
Patch-mainline: v5.18-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225
On some servers with MGA G200_SE_A (rev 42), booting with Legacy BIOS,
the hardware hangs when using kdump and kexec into the kdump kernel.
This happens when the uncompress code tries to write "Decompressing Linux"
to the VGA Console.
It can be reproduced by writing to the VGA console (0xB8000) after
booting to graphic mode, it generates the following error:
kernel:NMI: PCI system error (SERR) for reason a0 on CPU 0.
kernel:Dazed and confused, but trying to continue
The root cause is the configuration of the MGA GCTL6 register
According to the GCTL6 register documentation:
bit 0 is gcgrmode:
0: Enables alpha mode, and the character generator addressing system is
activated.
1: Enables graphics mode, and the character addressing system is not
used.
bit 1 is chainodd even:
0: The A0 signal of the memory address bus is used during system memory
addressing.
1: Allows A0 to be replaced by either the A16 signal of the system
address (ifmemmapsl is ‘00’), or by the hpgoddev (MISC<5>, odd/even
page select) field, described on page 3-294).
bit 3-2 are memmapsl:
Memory map select bits 1 and 0. VGA.
These bits select where the video memory is mapped, as shown below:
00 => A0000h - BFFFFh
01 => A0000h - AFFFFh
10 => B0000h - B7FFFh
11 => B8000h - BFFFFh
bit 7-4 are reserved.
Current code set it to 0x05 => memmapsl to b01 => 0xa0000 (graphic mode)
But on x86, the VGA console is at 0xb8000 (text mode)
In arch/x86/boot/compressed/misc.c debug strings are written to 0xb8000
As the driver doesn't use this mapping at 0xa0000, it is safe to set it to
0xb8000 instead, to avoid kernel hang on G200_SE_A rev42, with kexec/kdump.
Thus changing the value 0x05 to 0x0d
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Lyude Paul <lyude@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220119102905.1194787-1-jfalempe@redhat.com
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/mgag200/mgag200_mode.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
index b983541a4c53..cd9ba13ad5fc 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -529,7 +529,10 @@ static void mgag200_set_format_regs(struct mga_device *mdev,
WREG_GFX(3, 0x00);
WREG_GFX(4, 0x00);
WREG_GFX(5, 0x40);
- WREG_GFX(6, 0x05);
+ /* GCTL6 should be 0x05, but we configure memmapsl to 0xb8000 (text mode),
+ * so that it doesn't hang when running kexec/kdump on G200_SE rev42.
+ */
+ WREG_GFX(6, 0x0d);
WREG_GFX(7, 0x0f);
WREG_GFX(8, 0x0f);
--
2.38.1