linux-kernel - Re: [PATCH v7 01/10] iommu: Add DOMAIN_ATTR_MSI

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Message-ID: <57177A4E.4090804@arm.com>
Date:	Wed, 20 Apr 2016 13:47:10 +0100
From:	Robin Murphy <robin.murphy@....com>
To:	Eric Auger <eric.auger@...aro.org>, eric.auger@...com,
	alex.williamson@...hat.com, will.deacon@....com, joro@...tes.org,
	tglx@...utronix.de, jason@...edaemon.net, marc.zyngier@....com,
	christoffer.dall@...aro.org, linux-arm-kernel@...ts.infradead.org
Cc:	patches@...aro.org, linux-kernel@...r.kernel.org,
	Bharat.Bhushan@...escale.com, pranav.sawargaonkar@...il.com,
	p.fedin@...sung.com, iommu@...ts.linux-foundation.org,
	Jean-Philippe.Brucker@....com, julien.grall@....com
Subject: Re: [PATCH v7 01/10] iommu: Add DOMAIN_ATTR_MSI_MAPPING attribute

Hi Eric,

On 19/04/16 17:56, Eric Auger wrote:
> Introduce a new DOMAIN_ATTR_MSI_MAPPING domain attribute. If supported,
> this means the MSI addresses need to be mapped in the IOMMU.
>
> x86 IOMMUs typically don't expose the attribute since on x86, MSI write
> transaction addresses always are within the 1MB PA region [FEE0_0000h -
> FEF0_000h] window which directly targets the APIC configuration space and
> hence bypass the sMMU. On ARM and PowerPC however MSI transactions are
> conveyed through the IOMMU.

What's stopping us from simply inferring this from the domain's IOMMU 
not advertising interrupt remapping capabilities?

Robin.

> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@...escale.com>
> Signed-off-by: Eric Auger <eric.auger@...aro.org>
>
> ---
>
> v4 -> v5:
> - introduce the user in the next patch
>
> RFC v1 -> v1:
> - the data field is not used
> - for this attribute domain_get_attr simply returns 0 if the MSI_MAPPING
>    capability if needed or <0 if not.
> - removed struct iommu_domain_msi_maps
> ---
>   include/linux/iommu.h | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 62a5eae..b3e8c5b 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -113,6 +113,7 @@ enum iommu_attr {
>   	DOMAIN_ATTR_FSL_PAMU_ENABLE,
>   	DOMAIN_ATTR_FSL_PAMUV1,
>   	DOMAIN_ATTR_NESTING,	/* two stages of translation */
> +	DOMAIN_ATTR_MSI_MAPPING, /* Require MSIs mapping in iommu */
>   	DOMAIN_ATTR_MAX,
>   };
>
>