Re: [Xen-devel] [PATCH V3 5/8] iommu/arm: Add lightweight iommu_fwspec support

[Julien Grall <julien.grall@xxxxxxx>]

Hi Oleksandr,

On 8/20/19 7:09 PM, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>
> We need to have some abstract way to add new device to the IOMMU
> based on the generic IOMMU DT bindings [1] which can be used for
> both DT (right now) and ACPI (in future).
>
> For that reason we can borrow the idea used in Linux these days
> called "iommu_fwspec". Having this in, it will be possible
> to configure IOMMU master interfaces of the device (device IDs)
> from a single common place and avoid keeping almost identical look-up
> implementations in each IOMMU driver.
>
> There is no need to port the whole implementation of "iommu_fwspec"
> to Xen, we could, probably, end up with a much simpler solution,
> some "stripped down" version which fits our requirements.
>
> So, this patch adds the following:
> 1. A common structure "iommu_fwspec" to hold the the per-device
>     firmware data
> 2. New member "iommu_fwspec" of struct device
> 3. Functions/helpers to deal with "dev->iommu_fwspec"
>
> It should be noted that in comparing with original "iommu_fwspec"
s/comparing with/comparison of/
s/original/the Linux/ or "the original".

> Xen's variant doesn't contain some fields, which are not really
> needed at the moment (ops, flag) and "iommu_fwnode" field was replaced
> by "iommu_dev" to avoid porting a lot of code (to support "fwnode_handle")
> with little benefit.

It would be good to mention which version of Linux this is based on. So 
if there is a critical bug in Linux we can port it.
The rest of the patch looks good to me.

Cheers,

--
Julien Grall

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