mgag200 fix memmapsl configuration in GCTL6 register

mgag200 fix memmapsl configuration in GCTL6 register

[Jocelyn Falempe]

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

If some other architectures require the VGA memory to be at 0xA0000, I can
write another patch which won't change the memmapsl bits, (so assuming the
BIOS or UEFI already set it to the right value).
Another solution would be to set it to 0x0d only on x86.

Let me know what you think is the best way to fix it.

[PATCH] mgag200 fix memmapsl configuration in GCTL6 register

[Jocelyn Falempe]

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@redhat.com>
---
 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);
 
-- 
2.34.1

Re: [PATCH] mgag200 fix memmapsl configuration in GCTL6 register

[Javier Martinez Canillas]

Hello Jocelyn,

On 1/14/22 10:47, 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

I think this need some rewording after imirkin's explanation that 0xA0000 is the
address of the VGA video memory and 0xB8000 the address of the VGA text buffer.

> 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@redhat.com>
> ---
>  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);

My worry is if this could cause other issues so I would only do this change
if (is_kdump_kernel()), to make it as non intrusive as possible. And also
add a verbose comment about why this is needed.

If you make those changes, feel free to add:

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH] mgag200 fix memmapsl configuration in GCTL6 register

[Jocelyn Falempe]

On 18/01/2022 17:38, Javier Martinez Canillas wrote:
> Hello Jocelyn,
> 
> On 1/14/22 10:47, Jocelyn Falempe wrote:

> 
> My worry is if this could cause other issues so I would only do this change
> if (is_kdump_kernel()), to make it as non intrusive as possible. And also
> add a verbose comment about why this is needed.

This change must be done in the "first" kernel, so that when kdump 
starts, it doesn't hang the machine by writing to the VGA interface, in 
the early boot code.

To make this change less intrusive, we can do it only on problematic 
hardware (G200_SE rev 42), but Thomas said it was probably not needed.

> 
> If you make those changes, feel free to add:
> 
> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
> 
> Best regards,

Re: [PATCH] mgag200 fix memmapsl configuration in GCTL6 register

[Javier Martinez Canillas]

On 1/18/22 17:52, Jocelyn Falempe wrote:
> On 18/01/2022 17:38, Javier Martinez Canillas wrote:
>> Hello Jocelyn,
>>
>> On 1/14/22 10:47, Jocelyn Falempe wrote:
> 
>>
>> My worry is if this could cause other issues so I would only do this change
>> if (is_kdump_kernel()), to make it as non intrusive as possible. And also
>> add a verbose comment about why this is needed.
> 
> This change must be done in the "first" kernel, so that when kdump 
> starts, it doesn't hang the machine by writing to the VGA interface, in 
> the early boot code.
> 

Ah, got it. The patch then makes sense to me as is in that case.

My comment about documenting why this is needed still applies though.  

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH] mgag200 fix memmapsl configuration in GCTL6 register

[Jocelyn Falempe]

On 18/01/2022 18:17, Javier Martinez Canillas wrote:
> On 1/18/22 17:52, Jocelyn Falempe wrote:
>> On 18/01/2022 17:38, Javier Martinez Canillas wrote:
>>> Hello Jocelyn,
>>>
>>> On 1/14/22 10:47, Jocelyn Falempe wrote:
>>
>>>
>>> My worry is if this could cause other issues so I would only do this change
>>> if (is_kdump_kernel()), to make it as non intrusive as possible. And also
>>> add a verbose comment about why this is needed.
>>
>> This change must be done in the "first" kernel, so that when kdump
>> starts, it doesn't hang the machine by writing to the VGA interface, in
>> the early boot code.
>>
> 
> Ah, got it. The patch then makes sense to me as is in that case.
> 
> My comment about documenting why this is needed still applies though.

Yes, I will fix the commit message, and add a comment in the code.
I didn't know 0xA0000 was the graphic mode, so I though the 
configuration was a mistake.
But it turns out, the current configuration is good, but as the driver 
don't use this address, and kdump fails if this address is not VGA text 
mode on some hardware, it's better to set it to 0xb8000.

> 
> Best regards,

Thanks,

Re: [PATCH] mgag200 fix memmapsl configuration in GCTL6 register

[Lyude Paul]

We should probably  Cc: stable@vger.kernel.org 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@redhat.com>

I'd very much like Thomas Zimmerman to verify that this patch is OK though
with an R-b before we push anything upstream.

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@redhat.com>
> ---
>  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);
>  

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

Re: [PATCH] mgag200 fix memmapsl configuration in GCTL6 register

[Thomas Zimmermann]

[-- Attachment #1.1: Type: text/plain, Size: 3699 bytes --]

Hi

Am 18.01.22 um 20:06 schrieb Lyude Paul:
> We should probably  Cc: stable@vger.kernel.org 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@redhat.com>
> 
> 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@redhat.com>
>> ---
>>   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

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 840 bytes --]

[PATCH v2] mgag200 fix memmapsl configuration in GCTL6 register

[Jocelyn Falempe]

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
---

v2: Add clear statement that it's not the right configuration, but it
    prevents an annoying bug with kexec/kdump.

 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);
 
-- 
2.34.1

[PATCH v2] mgag200 fix memmapsl configuration in GCTL6 register

[Jocelyn Falempe]

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
---

v2: Add clear statement that it's not the right configuration, but it
    prevents an annoying bug with kexec/kdump.

 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);
 
-- 
2.34.1

Re: [PATCH v2] mgag200 fix memmapsl configuration in GCTL6 register

[Thomas Zimmermann]

[-- Attachment #1.1: Type: text/plain, Size: 3968 bytes --]

Hi,

Am 19.01.22 um 11:29 schrieb Jocelyn Falempe:
> 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
> ---
> 
> v2: Add clear statement that it's not the right configuration, but it
>      prevents an annoying bug with kexec/kdump.
> 
>   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);

Appears to be working on my test machine.

But please rune scripts/checkpatch.pl on the patch before sending it. I 
get several errors

WARNING: Possible unwrapped commit description (prefer a maximum 75 
chars per line)

#98:

     0: Enables alpha mode, and the character generator addressing system is



ERROR: trailing whitespace

#149: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:532:

+^I/* GCTL6 should be 0x05, but we configure memmapsl to 0xb8000 (text 
mode),^M$



ERROR: trailing whitespace

#150: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:533:

+^I * so that it doesn't hang when running kexec/kdump on G200_SE rev42.^M$




Best regards
Thomas


>   	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

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 840 bytes --]

Re: [PATCH v2] mgag200 fix memmapsl configuration in GCTL6 register

[Thomas Zimmermann]

[-- Attachment #1.1: Type: text/plain, Size: 3968 bytes --]

Hi,

Am 19.01.22 um 11:29 schrieb Jocelyn Falempe:
> 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
> ---
> 
> v2: Add clear statement that it's not the right configuration, but it
>      prevents an annoying bug with kexec/kdump.
> 
>   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);

Appears to be working on my test machine.

But please rune scripts/checkpatch.pl on the patch before sending it. I 
get several errors

WARNING: Possible unwrapped commit description (prefer a maximum 75 
chars per line)

#98:

     0: Enables alpha mode, and the character generator addressing system is



ERROR: trailing whitespace

#149: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:532:

+^I/* GCTL6 should be 0x05, but we configure memmapsl to 0xb8000 (text 
mode),^M$



ERROR: trailing whitespace

#150: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:533:

+^I * so that it doesn't hang when running kexec/kdump on G200_SE rev42.^M$




Best regards
Thomas


>   	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

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 840 bytes --]

Re: [PATCH v2] mgag200 fix memmapsl configuration in GCTL6 register

[Thomas Zimmermann]

[-- Attachment #1.1: Type: text/plain, Size: 1233 bytes --]

Hi

Am 19.01.22 um 13:21 schrieb Thomas Zimmermann:
> 
> Appears to be working on my test machine.
> 
> But please rune scripts/checkpatch.pl on the patch before sending it. I 
> get several errors
> 
> WARNING: Possible unwrapped commit description (prefer a maximum 75 
> chars per line)
> 
> #98:
> 
>      0: Enables alpha mode, and the character generator addressing 
> system is
> 
> 
> 
> ERROR: trailing whitespace
> 
> #149: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:532:
> 
> +^I/* GCTL6 should be 0x05, but we configure memmapsl to 0xb8000 (text 
> mode),^M$
> 
> 
> 
> ERROR: trailing whitespace
> 
> #150: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:533:
> 
> +^I * so that it doesn't hang when running kexec/kdump on G200_SE rev42.^M$
> 

Thanks a lot, the patch has been merge now. These problems might have 
been caused by my email client.

Best regards
Thomas

> 
> 
> 
> Best regards
> Thomas
> 
> 
>>       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

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 840 bytes --]

Re: [PATCH v2] mgag200 fix memmapsl configuration in GCTL6 register

[Thomas Zimmermann]

[-- Attachment #1.1: Type: text/plain, Size: 1233 bytes --]

Hi

Am 19.01.22 um 13:21 schrieb Thomas Zimmermann:
> 
> Appears to be working on my test machine.
> 
> But please rune scripts/checkpatch.pl on the patch before sending it. I 
> get several errors
> 
> WARNING: Possible unwrapped commit description (prefer a maximum 75 
> chars per line)
> 
> #98:
> 
>      0: Enables alpha mode, and the character generator addressing 
> system is
> 
> 
> 
> ERROR: trailing whitespace
> 
> #149: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:532:
> 
> +^I/* GCTL6 should be 0x05, but we configure memmapsl to 0xb8000 (text 
> mode),^M$
> 
> 
> 
> ERROR: trailing whitespace
> 
> #150: FILE: drivers/gpu/drm/mgag200/mgag200_mode.c:533:
> 
> +^I * so that it doesn't hang when running kexec/kdump on G200_SE rev42.^M$
> 

Thanks a lot, the patch has been merge now. These problems might have 
been caused by my email client.

Best regards
Thomas

> 
> 
> 
> Best regards
> Thomas
> 
> 
>>       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

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 840 bytes --]