linux-kernel - Re: [PATCH v3 2/3] iommu/tegra-smmu: Rework .probe_device and .attach

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Message-ID: <5945a63e-79d8-e3ae-ab53-cee8c220ac7d@gmail.com>
Date:   Thu, 1 Oct 2020 00:56:46 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>, joro@...tes.org,
        krzk@...nel.org, vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] iommu/tegra-smmu: Rework .probe_device and
 .attach_dev

01.10.2020 00:32, Nicolin Chen пишет:
> On Thu, Oct 01, 2020 at 12:24:25AM +0300, Dmitry Osipenko wrote:
>> ...
>>>> It looks to me like the only reason why you need this new global API is
>>>> because PCI devices may not have a device tree node with a phandle to
>>>> the IOMMU. However, SMMU support for PCI will only be enabled if the
>>>> root complex has an iommus property, right? In that case, can't we
>>>> simply do something like this:
>>>>
>>>> 	if (dev_is_pci(dev))
>>>> 		np = find_host_bridge(dev)->of_node;
>>>> 	else
>>>> 		np = dev->of_node;
>>>>
>>>> ? I'm not sure exactly what find_host_bridge() is called, but I'm pretty
>>>> sure that exists.
>>>>
>>>> Once we have that we can still iterate over the iommus property and do
>>>> not need to rely on this global variable.
>>>
>>> I agree that it'd work. But I was hoping to simplify the code
>>> here if it's possible. Looks like we have an argument on this
>>> so I will choose to go with your suggestion above for now.
>>
>> This patch removed more lines than were added. If this will be opposite
>> for the Thierry's suggestion, then it's probably not a great suggestion.
> 
> Sorry, I don't quite understand this comments. Would you please
> elaborate what's this "it" being "not a great suggestion"?
> 

I meant that you should try to implement Thierry's solution, but if the
end result will be worse than the current patch, then you shouldn't make
a v4, but get back to this discussion in order to choose the best option
and make everyone agree on it.