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

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Message-ID: <72b11925-5857-8ce5-d084-cab01ca1b396@gmail.com>
Date:   Thu, 1 Oct 2020 05:06:19 +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 04:26, Nicolin Chen пишет:
> On Thu, Oct 01, 2020 at 12:56:46AM +0300, Dmitry Osipenko wrote:
>> 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.
> 
> I see. Thanks for the reply. And here is a sample implementation:

That's what I supposed to happen :) The new variant adds code and
complexity, while old did the opposite. Hence the old variant is clearly
more attractive, IMO.