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

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Message-ID: <20200930161033.GE3833404@ulmo>
Date:   Wed, 30 Sep 2020 18:10:33 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...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

On Wed, Sep 30, 2020 at 06:36:52PM +0300, Dmitry Osipenko wrote:
>  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.

I don't think so. It's actually very clear and explicit. And yes, this
might be a little more work (and honestly, this is what? a handful of
lines?) than accessing a global variable, but that's a fair price to pay
for proper encapsulation.

> 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.

Also, this really proves the point I was trying to make about how this
is going to proliferate...

Thierry

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