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

[Jocelyn Falempe <jfalempe@redhat.com>]

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,

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