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

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Message-ID: <20201002010751.GA26971@Asurada-Nvidia>
Date:   Thu, 1 Oct 2020 18:07:51 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Dmitry Osipenko <digetx@...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

On Thu, Oct 01, 2020 at 11:33:38PM +0300, Dmitry Osipenko wrote:
> >>> If we can't come to an agreement on globalizing mc pointer, would
> >>> it be possible to pass tegra_mc_driver through tegra_smmu_probe()
> >>> so we can continue to use driver_find_device_by_fwnode() as v1?
> >>>
> >>> v1: https://lkml.org/lkml/2020/9/26/68
> >>
> >> tegra_smmu_probe() already takes a struct tegra_mc *. Did you mean
> >> tegra_smmu_probe_device()? I don't think we can do that because it isn't
> > 
> > I was saying to have a global parent_driver pointer: similar to
> > my v1, yet rather than "extern" the tegra_mc_driver, we pass it
> > through egra_smmu_probe() and store it in a static global value
> > so as to call tegra_smmu_get_by_fwnode() in ->probe_device().
> > 
> > Though I agree that creating a global device pointer (mc) might
> > be controversial, yet having a global parent_driver pointer may
> > not be against the rule, considering that it is common in iommu
> > drivers to call driver_find_device_by_fwnode in probe_device().
> 
> You don't need the global pointer if you have SMMU OF node.
> 
> You could also get driver pointer from mc->dev->driver.
> 
> But I don't think you need to do this at all. The probe_device() could
> be invoked only for the tegra_smmu_ops and then seems you could use
> dev_iommu_priv_set() in tegra_smmu_of_xlate(), like sun50i-iommu driver
> does.

Getting iommu device pointer using driver_find_device_by_fwnode()
is a common practice in ->probe_device() of other iommu drivers.
But this requires a device_driver pointer that tegra-smmu doesn't
have. So passing tegra_mc_driver through tegra_smmu_probe() will
address it.