Re: further issues with MGA G200 graphics chipset

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 28.04.26 um 21:12 schrieb stuart hayes:
> On 4/27/2026 7:14 AM, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 25.04.26 um 01:29 schrieb Jacob Keller:
>> [...]
>>>>
>>>> So I suggest to pick Manufacturer, Product, Version as key. I'd be
>>>> surprised if we find more than a hand full of systems with the 
>>>> issue. If
>>>> we see a trend or common pattern, we can generalize later on.
>>>>
>>> I think this is the best solution. Keep it focused for now. I believe
>>> Intel has two major platforms that we care about with respect to this
>>> issue. I'll see if I can dig up the data. The systems install the MGA
>>> G200 for BMC use but don't seem to expose the VGA connection.
>>>
>>> For the specific system I have that was faulty, we have the following:
>>>
>>> $ for t in system-manufacturer system-product-name system-version ; \
>>>      do dmidecode -s ${t}; \
>>> done
>>> Dell Inc.
>>> PowerEdge XR8720t
>>> Not Specified
>>>
>>>
>>>
>>> I believe there was also some concern about HP systems which similarly
>>> use this chipset, but I don't have the DMI data for that one off hand.
>>> I've asked some colleagues to confirm the situation and obtain that
>>> data. I'll get back early next week if we think there are any other
>>> systems possibly affected.
>>>
>>> In the mean time, I'm happy to have our team test any patch to confirm
>>> that it behaves as expected and resolves the service interruptions.
>>
>> For now, I've modified the two places that have BMC support in the 
>> driver. Could you please also tell me your system's exact Matrox 
>> chipset or its PCI id?
>>
>> The patch is attached for your testing. It would work against drm-tip 
>> or v7.1-rc1.
>>
>> I've also found the page at [1], which claims that there's a Mini-DP 
>> port at the front. If so, I'd assume that there's also an extra 
>> encoder chip to replace the VGA. If we ever get specs for that, we 
>> could implement real support in the driver.
>>
>> In the meantime, the current fix should work. In the worst case, that 
>> Mini-DP port would give a lower default resolution.
>>
>> [1] https://www.dell.com/en-us/shop/ipovw/poweredge-xr8720t? 
>> hve=shop+now#techspecs_section
>>
>> Best regards
>> Thomas
>>
>>
>
> So this patch disables DDC polling if the dmi_check_system() matches. 
> If this was to happen on systems that _do_ have a physical VGA 
> connector, will that port still be active, just with a resolution that 
> may not be compatible with the monitor that's plugged in?

The DMI test is supposed to only match on affected systems. If there's a 
matched system with a VGA port, or possibly that Mini-DP port, users 
will get a number of bogus display modes at the worst. But the default 
mode is 1024x768, which should work on any display.

>
> I don't see anyone say that the DDC polling doesn't cause too much 
> latency for real time kernels on other systems that do have a VGA 
> connector... did I miss that, or is there a chance that a lot of other 
> systems that use this driver might also have issues with a real time 
> kernel?
That missing VGA port is a problem on any workload. So we fix it as far 
as possible. Where the connector polling interferes with RT, it can also 
be disabled with drm_kms_helper.poll=0. Best regards Thomas
>
>
>>
>>
>>>
>>> Appreciate all the feedback on this thread.
>>>
>>> Thanks,
>>> Jake
>>
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)