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

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Message-ID: <20200930160626.GD3833404@ulmo>
Date:   Wed, 30 Sep 2020 18:06:26 +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.
> 
> 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.

Why do we need it there? They seem to work fine without it right now. If
it is required for new functionality, we can always make the dependent
on a DT reference via phandle without breaking any existing code.

Thierry

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