linux-kernel - Re: [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers

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Date:   Fri, 1 Nov 2019 10:27:59 +0000
From:   John Garry <john.garry@...wei.com>
To:     Saravana Kannan <saravanak@...gle.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "Will Deacon" <will@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers

On 31/10/2019 23:34, Saravana Kannan via iommu wrote:
> I looked into the iommu-map property and it shouldn't be too hard to
> add support for it. Looks like we can simply hold off on probing the
> root bridge device till all the iommus in its iommu-map are probed and
> we should be fine.
> 
>> I'm also unsure about distro vendors agreeing to a mandatory kernel
>> parameter (of_devlink). Do you plan to eventually enable it by default?
>>
>>> static const struct supplier_bindings of_supplier_bindings[] = {
>>>          { .parse_prop = parse_clocks, },
>>>          { .parse_prop = parse_interconnects, },
>>>          { .parse_prop = parse_regulators, },
>>> +        { .parse_prop = parse_iommus, },
>>>          {},
>>> };
>>>
>>> I plan to upstream this pretty soon, but I have other patches in
>>> flight that touch the same file and I'm waiting for those to get
>>> accepted. I also want to clean up the code a bit to reduce some
>>> repetition before I add support for more bindings.
>> I'm also wondering about ACPI support.
> I'd love to add ACPI support too, but I have zero knowledge of ACPI.
> I'd be happy to help anyone who wants to add ACPI support that allows
> ACPI to add device links.

If possible to add, that may be useful for remedying this:

https://lore.kernel.org/linux-iommu/9625faf4-48ef-2dd3-d82f-931d9cf26976@huawei.com/

Thanks,
John

> 
>> IOMMU already has a sort of
>> canonical code path that links endpoints to their IOMMU
>> (iommu_probe_device()), after the firmware descriptions have been parsed.
>> So if we created the device links in the iommu core, for example
>> iommu_bus_notifier(), we would support all firmware interface fl