Re: 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

Best regards
Thomas

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

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 (wangyu...@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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