linux-kernel - Re: [PATCH v7 1/7] iommu/arm-smmu-v3: Make default domain type of HiSilicon PTT device to identity

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Date:   Tue, 10 May 2022 12:23:27 +0100
From:   Will Deacon <will@...nel.org>
To:     Yicong Yang <yangyicong@...ilicon.com>
Cc:     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
Subject: Re: [PATCH v7 1/7] iommu/arm-smmu-v3: Make default domain type of
 HiSilicon PTT device to identity

On Thu, Apr 07, 2022 at 08:58:35PM +0800, Yicong Yang wrote:
> The DMA operations of HiSilicon PTT device can only work properly with
> identical mappings. So add a quirk for the device to force the domain
> as 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(+)

I still don't like this being part of the SMMU driver, but given that
(a) Robin doesn't seem to agree with the objection and (b) you've been
refreshing the patch series:

Acked-by: Will Deacon <will@...nel.org>

If you do respin, then:

> 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 627a3ed5ee8f..5ec15ae2a9b1 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2839,6 +2839,21 @@ static int arm_smmu_dev_disable_feature(struct device *dev,
>  	}
>  }

It might be worth adding a brief comment here to explain what this device is
and why it needs an identity mapping.

> +#define IS_HISI_PTT_DEVICE(pdev)	((pdev)->vendor == PCI_VENDOR_ID_HUAWEI && \
> +					 (pdev)->device == 0xa12e)

Will