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Subject: Re: [PATCH 1/8] iommu/vt-d: clean up 32bit si_domain assignment
To:     Tom Murphy <murphyt7@tcd.ie>, iommu@lists.linux-foundation.org
References: <20191221150402.13868-1-murphyt7@tcd.ie>
 <20191221150402.13868-2-murphyt7@tcd.ie>
From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <e569e246-11a1-e8bd-9347-310284e96885@linux.intel.com>
Date:   Mon, 23 Dec 2019 11:00:47 +0800
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Hi,

On 12/21/19 11:03 PM, Tom Murphy wrote:
> @@ -5618,9 +5583,13 @@ static int intel_iommu_add_device(struct device *dev)
>   	struct iommu_domain *domain;
>   	struct intel_iommu *iommu;
>   	struct iommu_group *group;
> +	u64 dma_mask = *dev->dma_mask;
>   	u8 bus, devfn;
>   	int ret;
>   
> +	if (dev->coherent_dma_mask && dev->coherent_dma_mask < dma_mask)
> +		dma_mask = dev->coherent_dma_mask;
> +
>   	iommu = device_to_iommu(dev, &bus, &devfn);
>   	if (!iommu)
>   		return -ENODEV;
> @@ -5640,7 +5609,12 @@ static int intel_iommu_add_device(struct device *dev)
>   	domain = iommu_get_domain_for_dev(dev);
>   	dmar_domain = to_dmar_domain(domain);
>   	if (domain->type == IOMMU_DOMAIN_DMA) {
> -		if (device_def_domain_type(dev) == IOMMU_DOMAIN_IDENTITY) {
> +		/*
> +		 * We check dma_mask >= dma_get_required_mask(dev) because
> +		 * 32 bit DMA falls back to non-identity mapping.
> +		 */
> +		if (device_def_domain_type(dev) == IOMMU_DOMAIN_IDENTITY &&
> +				dma_mask >= dma_get_required_mask(dev)) {
>   			ret = iommu_request_dm_for_dev(dev);
>   			if (ret) {
>   				dmar_remove_one_dev_info(dev);

dev->dma_mask is set to 32bit by default. During loading driver, it sets
the real dma_mask with dma_set_mask() according to the real capability.
Here you will always see 32bit dma_mask for each device.

Best regards,
baolu