[PATCH v6 2/3] arm64: Add IOMMU dma_ops

[Anup Patel]

On Wed, Oct 7, 2015 at 10:06 PM, Robin Murphy <robin.murphy at arm.com> wrote:
> On 07/10/15 10:03, Anup Patel wrote:
> [...]
>
>>> +static bool do_iommu_attach(struct device *dev, const struct iommu_ops
>>> *ops,
>>> +                          u64 dma_base, u64 size)
>>> +{
>>> +       struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
>>> +
>>> +       /*
>>> +        * Best case: The device is either part of a group which was
>>> +        * already attached to a domain in a previous call, or it's
>>> +        * been put in a default DMA domain by the IOMMU core.
>>> +        */
>>> +       if (!domain) {
>>> +               /*
>>> +                * Urgh. The IOMMU core isn't going to do default domains
>>> +                * for non-PCI devices anyway, until it has some means of
>>> +                * abstracting the entirely implementation-specific
>>> +                * sideband data/SoC topology/unicorn dust that may or
>>> +                * may not differentiate upstream masters.
>>> +                * So until then, HORRIBLE HACKS!
>>> +                */
>>> +               domain = ops->domain_alloc(IOMMU_DOMAIN_DMA);
>>> +               if (!domain)
>>> +                       goto out_no_domain;
>>> +
>>> +               domain->ops = ops;
>>> +               domain->type = IOMMU_DOMAIN_DMA |
>>> __IOMMU_DOMAIN_FAKE_DEFAULT;
>>
>>
>> We require iommu_get_dma_cookie(domain) here. If we dont
>> allocate iommu cookie then iommu_dma_init_domain() will fail.
>
>
> The iova cookie is tightly coupled with the domain, so it really only makes
> sense for the IOMMU driver to deal with it as part of its
> domain_alloc/domain_free callbacks.
>
> Doing that here was one of the nastier 'compatibility' hacks which I've now
> taken out; trying to make things work without modifying existing IOMMU
> drivers was just too impractical. Drivers which want to play are now
> required to support the IOMMU_DOMAIN_DMA type appropriately, but it's still
> only a minimal change, as per the example diff for the ARM SMMU driver below
> (big pile of further patches necessary to make said driver compatible in
> other respects notwithstanding).

Many thanks for the info.

Actually, I was trying your dma-mapping patches with SMMU driver. I have got
SMMU driver somewhat working for IOMMU_DOMAIN_DMA. Your suggestion
will help me restrict my changes to SMMU driver only.

This patchset looks good to me.

Thanks,
Anup