mgag200 broken on kernel-6.0-rc3 on DELL/T620

[Thomas Zimmermann]

Hi

Am 14.09.22 um 16:58 schrieb Wang Yugui:
> Hi,
> 
>> (cc: Jocelyn)
>>
>> Hi
>>
>> Am 14.09.22 um 10:29 schrieb Wang Yugui:
>>> Hi,
>>>
>>>
>>>> Hi
>>>>
>>>> Am 13.09.22 um 17:15 schrieb Wang Yugui:
>>>> [...]
>>>>>>>
>>>>>>> so I tried to revert patch of mgag200 driver in batch of 2 or 3, the I
>>>>>>> noticed the patch 'Subject: drm/mgag200: Remove special case for G200SE
>>>>>>> with <2 MiB' and then tried this dirty fix.
>>>>>>
>>>>>> Oh, great work! Thank you. From looking at the screenshot that you provided, it seems as if the 24-bit mode setting is broken. I'm not sure why the G200SE workaround applies to a G200ER, but we'll see.
>>>>>
>>>>> I tested 'preferred_depth = 32' too. it works on T630 too.
>>>>>
>>>>> so both 16 and 32 work, but 24 failed on DELL/T630.
>>>>
>>>> I tried on my test machine with a 5.19 kernel and found that 32-bit and 24-bit pixels work, but 16-bit looks incorrect.
>>>>
>>>> What are the results if you boot your kernel 5.19.3 with the parameter video=1024x768-24? This should enable 24-bit pixels.
>>>>
>>>> How does video=1024x768-16 look with the 5.19 kernel?
>>>
>>> test result here
>>> kernel 5.19.3 & video=1024x768-24
>>> 	dell/T620/centos-8.5	broken
>>> 	dell/T630/centos-7.9	broken
>>
>> I assume that Centos 7 and 8 have fairly old kernels? So it's been a long-standing bug.
> 
> We install kernel 5.19.3/5.15.67 into Centos 7 and 8.
> default it work well.  broken just when 'video=1024x768-24', so it may
> not a long-standing bug.

I don't quite understand. Does 'video=1024x768-24' work with 5.15.67?

> 
>> 24-bit works on my G200HE and G200 test machines. Maybe the G200ER has a bug.
>>
>> When I try 16-bit depth, the display works, but is way too dark. No fiddling with the LUT tables fixes this. It's 90s hardware, so it should support 16-bit framebuffers well, but there's no obvious bug to be seen.
>>
>> I guess, we could remove 16 and 24 bit support for now if nothing else helps.
> 
> 
> maybe better if we revert 73f54d5d9682 (drm/mgag200: Remove special case
> for G200SE with <2 MiB)
> 
> because there is no test result on device G200_SE

We cannot revert it directly, but tomorrow I'll send you a patch that 
should restore the old behavior.

Best regards
Thomas

> 
> static unsigned int mgag200_preferred_depth(struct mga_device *mdev)
> {
>         if (IS_G200_SE(mdev) && mdev->vram_fb_available < (2048*1024))
>                 return 16;
>         else
>                 return 32;
> }
> 
> Best Regards
> Wang Yugui (wangyugui at e16-tech.com)
> 2022/09/14
> 

-- 
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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