linux-kernel - Re: [PATCH 3/8] iommu/arm-smmu-v3: Support platform SSID

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Message-ID: <73cfb797-5ae7-b9d9-01ea-fe98a1bed5c3@arm.com>
Date:   Wed, 19 Jun 2019 12:53:46 +0100
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Will Deacon <will.deacon@....com>
Cc:     "joro@...tes.org" <joro@...tes.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        Robin Murphy <Robin.Murphy@....com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>
Subject: Re: [PATCH 3/8] iommu/arm-smmu-v3: Support platform SSID

On 18/06/2019 19:08, Will Deacon wrote:
>> +	/*
>> +	 * If the SMMU doesn't support 2-stage CD, limit the linear
>> +	 * tables to a reasonable number of contexts, let's say
>> +	 * 64kB / sizeof(ctx_desc) = 1024 = 2^10
>> +	 */
>> +	if (!(smmu->features & ARM_SMMU_FEAT_2_LVL_CDTAB))
>> +		master->ssid_bits = min(master->ssid_bits, 10U);
> 
> Please introduce a #define for the 10, so that it is computed in the way
> you describe in the comment (a bit like we do for things like queue sizes).

Ok

>> +
>>  	group = iommu_group_get_for_dev(dev);
>>  	if (!IS_ERR(group)) {
>>  		iommu_group_put(group);
>> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
>> index f04a6df65eb8..04f4f6b95d82 100644
>> --- a/drivers/iommu/of_iommu.c
>> +++ b/drivers/iommu/of_iommu.c
>> @@ -206,8 +206,12 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
>>  			if (err)
>>  				break;
>>  		}
>> -	}
>>  
>> +		fwspec = dev_iommu_fwspec_get(dev);
>> +		if (!err && fwspec)
>> +			of_property_read_u32(master_np, "pasid-num-bits",
>> +					     &fwspec->num_pasid_bits);
>> +	}
> 
> Hmm. Do you know if there's anything in ACPI for this?

Yes, IORT version D introduced a "substream width" field for the Named
component node (platform device). I don't think it existed last time I
checked, so I'll see about supporting it.

Thanks,
Jean