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

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Date:   Mon, 5 Oct 2020 12:38:20 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Nicolin Chen <nicoleotsuka@...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

05.10.2020 12:16, Thierry Reding пишет:
...
>> I think you meant regmap in regards to protecting IO accesses, but this
>> is not what regmap is about if IO accesses are atomic by nature.
> 
> Then why is there regmap-mmio?

To protect programming sequences for example, actually that's the only
real use-case I saw in kernel drivers once. In our case there are no
sequences that require protection, at least I'm not aware about that.

>> Secondly, you're missing that tegra30-devfreq driver will also need to
>> perform the MC lookup [3] and then driver will no longer work for the
>> older DTs if phandle becomes mandatory because these DTs do not have the
>> MC phandle in the ACTMON node.
>>
>> [3]
>> https://github.com/grate-driver/linux/commit/441d19281f9b3428a4db1ecb3a02e1ec02a8ad7f
>>
>> So we will need the fall back for T30/124 as well.
> 
> No, we don't need the fallback because this is new functionality which
> can and should be gated on the existence of the new phandle. If there's
> no phandle then we have no choice but to use the old code to ensure old
> behaviour.

You just repeated what I was trying to say:)

Perhaps I spent a bit too much time touching that code to the point that
lost feeling that there is a need to clarify everything in details.