Hi Am 18.01.22 um 20:06 schrieb Lyude Paul:
We should probably Cc: stable@xxxxxxxxxxxxxxx this as well, see: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for more info. As well, some useful tools for adding the appropriate Fixes: tags: https://drm.pages.freedesktop.org/maintainer-tools/dim.html At least on my end this is: Acked-by: Lyude Paul <lyude@xxxxxxxxxx> I'd very much like Thomas Zimmerman to verify that this patch is OK though with an R-b before we push anything upstream.
Yep, I'll give it a try on my test system. I'll also add a TODO comment that summarizes the situation.
A real fix would detect that the kdump kernel is running and not use the display then.
Best regards Thomas
On Fri, 2022-01-14 at 10:47 +0100, Jocelyn Falempe wrote:On some server with MGA G200e (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 a bad 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 (if memmapsl 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 driver code set it to 0x05 => memmapsl to b01 => 0xA0000 but on x86, the VGA console is at 0xB8000 arch/x86/boot/compressed/misc.c define vidmem to 0xb8000 in extract_kernel() so it's better to configure it to b11 Thus changing the value 0x05 to 0x0d Signed-off-by: Jocelyn Falempe <jfalempe@xxxxxxxxxx> --- drivers/gpu/drm/mgag200/mgag200_mode.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c index b983541a4c53..c7f63610b278 100644 --- a/drivers/gpu/drm/mgag200/mgag200_mode.c +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c @@ -529,7 +529,7 @@ 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); + WREG_GFX(6, 0x0d); WREG_GFX(7, 0x0f); WREG_GFX(8, 0x0f);
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
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