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

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

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@xxxxxxxxxx]
> > Sent: Wednesday, June 08, 2022 9:17 PM
> > To: Kuo-Hsiang Chou <kuohsiang_chou@xxxxxxxxxxxxxx>; Thomas Zimmermann 
> > <tzimmermann@xxxxxxx>; airlied@xxxxxxxxxx; airlied@xxxxxxxx; 
> > daniel@xxxxxxxx; regressions@xxxxxxxxxxxxx
> > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; Luke Chen 
> > <luke_chen@xxxxxxxxxxxxxx>; Hungju Huang 
> > <hungju_huang@xxxxxxxxxxxxxx>; Charles Kuan <charles_kuan@xxxxxxxxxxxxxx>
> > 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@xxxxxxx]
> > >
> > > Sent: Tuesday, June 07, 2022 8:03 PM
> > >
> > > To: airlied@xxxxxxxxxx; airlied@xxxxxxxx; daniel@xxxxxxxx;
> > > jfalempe@xxxxxxxxxx; regressions@xxxxxxxxxxxxx; Kuo-Hsiang Chou
> > > <kuohsiang_chou@xxxxxxxxxxxxxx>
> > >
> > > 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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