linux-kernel - Re: [PATCH v3 8/8] iommu/arm-smmu-v3: Make default domain type of HiSilicon PTT device to identity

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Message-ID: <20220215130044.GA7154@willie-the-truck>
Date:   Tue, 15 Feb 2022 13:00:44 +0000
From:   Will Deacon <will@...nel.org>
To:     Yicong Yang <yangyicong@...wei.com>
Cc:     Yicong Yang <yangyicong@...ilicon.com>, gregkh@...uxfoundation.org,
        helgaas@...nel.org, alexander.shishkin@...ux.intel.com,
        lorenzo.pieralisi@....com, mark.rutland@....com,
        mathieu.poirier@...aro.org, suzuki.poulose@....com,
        mike.leach@...aro.org, leo.yan@...aro.org,
        jonathan.cameron@...wei.com, daniel.thompson@...aro.org,
        joro@...tes.org, john.garry@...wei.com,
        shameerali.kolothum.thodi@...wei.com, robin.murphy@....com,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        coresight@...ts.linaro.org, linux-pci@...r.kernel.org,
        linux-perf-users@...r.kernel.org, iommu@...ts.linux-foundation.org,
        prime.zeng@...wei.com, liuqi115@...wei.com,
        zhangshaokun@...ilicon.com, linuxarm@...wei.com,
        song.bao.hua@...ilicon.com
Subject: Re: [PATCH v3 8/8] iommu/arm-smmu-v3: Make default domain type of
 HiSilicon PTT device to identity

On Mon, Feb 14, 2022 at 08:55:20PM +0800, Yicong Yang wrote:
> On 2022/1/24 21:11, Yicong Yang wrote:
> > The DMA of HiSilicon PTT device can only work with identical
> > mapping. So add a quirk for the device to force the domain
> > passthrough.
> > 
> > Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> > ---
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > index 6dc6d8b6b368..6f67a2b1dd27 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -2838,6 +2838,21 @@ static int arm_smmu_dev_disable_feature(struct device *dev,
> >  	}
> >  }
> >  
> > +#define IS_HISI_PTT_DEVICE(pdev)	((pdev)->vendor == PCI_VENDOR_ID_HUAWEI && \
> > +					 (pdev)->device == 0xa12e)
> > +
> > +static int arm_smmu_def_domain_type(struct device *dev)
> > +{
> > +	if (dev_is_pci(dev)) {
> > +		struct pci_dev *pdev = to_pci_dev(dev);
> > +
> > +		if (IS_HISI_PTT_DEVICE(pdev))
> > +			return IOMMU_DOMAIN_IDENTITY;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static struct iommu_ops arm_smmu_ops = {
> >  	.capable		= arm_smmu_capable,
> >  	.domain_alloc		= arm_smmu_domain_alloc,
> > @@ -2863,6 +2878,7 @@ static struct iommu_ops arm_smmu_ops = {
> >  	.sva_unbind		= arm_smmu_sva_unbind,
> >  	.sva_get_pasid		= arm_smmu_sva_get_pasid,
> >  	.page_response		= arm_smmu_page_response,
> > +	.def_domain_type	= arm_smmu_def_domain_type,
> >  	.pgsize_bitmap		= -1UL, /* Restricted during device attach */
> >  	.owner			= THIS_MODULE,
> >  };
> > 
>
> Is this quirk ok with the SMMU v3 driver? Just want to confirm that I'm on the
> right way to dealing with the issue of our device.

I don't think the quirk should be in the SMMUv3 driver. Assumedly, you would
have the exact same problem if you stuck the PTT device behind a different
type of IOMMU, and so the quirk should be handled by a higher level of the
stack.

Will