Re: [PATCH] drm/ast: Treat AST2600 like AST2500 in most places

[Thomas Zimmermann <tzimmermann@suse.de>]

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Am 09.06.22 um 09:06 schrieb Jocelyn Falempe:
> On 09/06/2022 04:32, Kuo-Hsiang Chou wrote:
>> Hi Jocelyn Falempe,
>>
>> -----Original Message-----
>> From: Jocelyn Falempe [mailto:jfalempe@redhat.com]
>> Sent: Wednesday, June 08, 2022 9:17 PM
>> To: Kuo-Hsiang Chou <kuohsiang_chou@aspeedtech.com>; Thomas Zimmermann 
>> <tzimmermann@suse.de>; airlied@redhat.com; airlied@linux.ie; 
>> daniel@ffwll.ch; regressions@leemhuis.info
>> Cc: dri-devel@lists.freedesktop.org; stable@vger.kernel.org; Luke Chen 
>> <luke_chen@aspeedtech.com>; Hungju Huang 
>> <hungju_huang@aspeedtech.com>; Charles Kuan <charles_kuan@aspeedtech.com>
>> Subject: Re: [PATCH] drm/ast: Treat AST2600 like AST2500 in most places
>>
>> On 08/06/2022 10:09, Kuo-Hsiang Chou wrote:
>>> Hi Thomas
>>>
>>> Thanks for your suggestions!
>>>
>>> I answer each revision inline that followed by [KH]:.
>>
>> Thanks for reviewing this.
>>>
>>> Regards,
>>>
>>>           Kuo-Hsiang Chou
>>>
>>> -----Original Message-----
>>>
>>> From: Thomas Zimmermann [mailto:tzimmermann@suse.de]
>>>
>>> Sent: Tuesday, June 07, 2022 8:03 PM
>>>
>>> To: airlied@redhat.com; airlied@linux.ie; daniel@ffwll.ch;
>>> jfalempe@redhat.com; regressions@leemhuis.info; Kuo-Hsiang Chou
>>> <kuohsiang_chou@aspeedtech.com>
>>>
>>> Subject: [PATCH] drm/ast: Treat AST2600 like AST2500 in most places
>>>
>>> Include AST2600 in most of the branches for AST2500. Thereby revert
>>> most effects of commit f9bd00e0ea9d ("drm/ast: Create chip AST2600").
>>>
>>> The AST2600 used to be treated like an AST2500, which at least gave
>>> usable display output. After introducing AST2600 in the driver without
>>> further updates, lots of functions take the wrong branches.
>>>
>>> Handling AST2600 in the AST2500 branches reverts back to the original
>>> settings. The exception are cases where AST2600 meanwhile got its own
>>> branch.
>>>
>>> [KH]: Based on CVE_2019_6260 item3, P2A is disallowed anymore.
>>>
>>> P2A (PCIe to AMBA) is a bridge that is able to revise any BMC registers.
>>>
>>> Yes, P2A is dangerous on security issue, because Host open a backdoor
>>> and someone malicious SW/APP will be easy to take control of BMC.
>>>
>>> Therefore, P2A is disabled forever.
>>>
>>> Now, return to this patch, there is no need to add AST2600 condition
>>> on the P2A flow.
>>>
>>
>> [snip]
>>>
>>> [KH]: Yes, the patch is "drm/ast: Create threshold values for AST2600"
>>> that is the root cause of whites lines on AST2600
>>>
>>> commit
>>>
>>>
>>> bcc77411e8a65929655cef7b63a36000724cdc4b
>>> <https://cgit.freedesktop.org/drm/drm/commit/?id=bcc77411e8a65929655ce
>>> f7b63a36000724cdc4b> (patch
>>> <https://cgit.freedesktop.org/drm/drm/patch/?id=bcc77411e8a65929655cef
>>> 7b63a36000724cdc4b>)
>>>
>>
>>
>> So basically this commit should be enough to fix the white lines  and 
>> flickering with VGA output on AST2600 ?
>> [KH]: Yes.
>>     You are welcome to tell me something if you consider there is 
>> other strange issue.
>>     Thanks for your efforts on drm/ast project!
>> Regards,
>>     Kuo-Hsiang Chou
> 
> I've got confirmation that this commit is enough to fix the issue 
> introduced with f9bd00e0ea9d.
> 
> So let's drop this patch, and submit bcc77411e8a6 "drm/ast: Create 
> threshold values for AST2600" to stable kernel instead.

Thanks to both of you for your help with this bug.

Best regards
Thomas

> 
> Thanks,
> 
>>
>> I will try to have it tested, and if it's good, we may want to have it 
>> on stable kernel.
>>
>> Best regards,
>>
> 

-- 
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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