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Date:   Thu, 14 Dec 2023 11:46:35 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Lyude Paul <lyude@redhat.com>
Cc:     dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        Karol Herbst <kherbst@redhat.com>,
        Danilo Krummrich <dakr@redhat.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Ben Skeggs <bskeggs@redhat.com>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] drm/nouveau/kms/nv50-: Don't allow inheritance of
 headless iors
Message-ID: <20231214104635.GAZXrdC7G6RMlIjxE/@fat_crate.local>
References: <20231214004359.1028109-1-lyude@redhat.com>
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In-Reply-To: <20231214004359.1028109-1-lyude@redhat.com>
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On Wed, Dec 13, 2023 at 07:43:57PM -0500, Lyude Paul wrote:
> Turns out we made a silly mistake when coming up with OR inheritance on
> nouveau. On pre-DCB 4.1, iors are statically routed to output paths via the
> DCB. On later generations iors are only routed to an output path if they're
> actually being used. Unfortunately, it appears with NVIF_OUTP_INHERIT_V0 we
> make the mistake of assuming the later is true on all generations, which is
> currently leading us to return bogus ior -> head assignments through nvif,
> which causes WARN_ON().
> 
> So - fix this by verifying that we actually know that there's a head
> assigned to an ior before allowing it to be inherited through nvif. This
> -should- hopefully fix the WARN_ON on GT218 reported by Borislav.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> ---
>  drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c b/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c
> index e4279f1772a1b..377d0e0cef848 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c
> @@ -385,7 +385,7 @@ nvkm_uoutp_mthd_inherit(struct nvkm_outp *outp, void *argv, u32 argc)
>  
>  	/* Ensure an ior is hooked up to this outp already */
>  	ior = outp->func->inherit(outp);
> -	if (!ior)
> +	if (!ior || !ior->arm.head)
>  		return -ENODEV;
>  
>  	/* With iors, there will be a separate output path for each type of connector - and all of
> -- 

Thanks, that fixes it!

Reported-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette