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

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Message-ID: <ece615ad-8d6b-96ae-d8b4-9667aef17281@gmail.com>
Date:   Wed, 30 Sep 2020 18:36:52 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Nicolin Chen <nicoleotsuka@...il.com>
Cc:     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

 I'...
>> +	struct tegra_mc *mc = devm_tegra_get_memory_controller(dev);
>> +	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> 
> 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.

This sounds more complicated than the current variant.

Secondly, I'm already about to use the new tegra_get_memory_controller()
API for all the T20/30/124/210 EMC and devfreq drivers.