linux-kernel - Re: [PATCH] iommu/amd: Fix amd_iommu_detect() (does not fix any issues).

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Message-ID: <20151026160717.GF5618@l.oracle.com>
Date:	Mon, 26 Oct 2015 12:07:17 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	j.glisse@...il.com
Cc:	linux-kernel@...r.kernel.org,
	Jérôme Glisse <jglisse@...hat.com>,
	Joerg Roedel <jroedel@...e.de>,
	iommu@...ts.linux-foundation.org
Subject: Re: [PATCH] iommu/amd: Fix amd_iommu_detect() (does not fix any
 issues).

On Mon, Aug 31, 2015 at 06:13:03PM -0400, j.glisse@...il.com wrote:
> From: Jérôme Glisse <jglisse@...hat.com>
> 
> Fix amd_iommu_detect() to return positive value on success, like
> intended, and not zero. This will not change anything in the end
> as AMD IOMMU disable swiotlb and properly associate itself with

Not sure how it disables SWIOTLB? The AMD Vi does not seem to
change 'swiotlb'. While 'gart_iommu_init' does. Did you mean
the AMD GART code?

> devices even if detect() doesn't return a positive value.

Returning positive will mean that the pci_iommu_alloc will stop
processing _all_ other IOMMUs.

While returning 0 will let it detect the other IOMMUs.

Granted on an AMD machine there can be two 'IOMMU's - the GART
and the AMD Vi. The detection is always to call gart_iommu_hole_init
first, then amd_iommu_detect.

I presume if there was one more type on AMD we would run into trouble.

> 
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: iommu@...ts.linux-foundation.org
> ---
>  drivers/iommu/amd_iommu_init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> index a24495e..360a451 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -2198,7 +2198,7 @@ int __init amd_iommu_detect(void)
>  	iommu_detected = 1;
>  	x86_init.iommu.iommu_init = amd_iommu_init;
>  
> -	return 0;
> +	return 1;
>  }
>  
>  /****************************************************************************
> -- 
> 1.8.3.1
> 
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
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