linux-kernel - Re: [PATCH v2 2/3] iommu/tegra-smmu: Rework .probe_device and .attach

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Message-ID: <20200930061935.GB16460@Asurada-Nvidia>
Date:   Tue, 29 Sep 2020 23:19:35 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     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 v2 2/3] iommu/tegra-smmu: Rework .probe_device and
 .attach_dev

On Wed, Sep 30, 2020 at 08:59:45AM +0300, Dmitry Osipenko wrote:
> 30.09.2020 08:41, Nicolin Chen пишет:
> > On Wed, Sep 30, 2020 at 08:39:54AM +0300, Dmitry Osipenko wrote:
> >> 30.09.2020 03:30, Nicolin Chen пишет:
> >>>  static int tegra_smmu_attach_dev(struct iommu_domain *domain,
> >>>  				 struct device *dev)
> >>>  {
> >>> +	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> >>>  	struct tegra_smmu *smmu = dev_iommu_priv_get(dev);
> >>>  	struct tegra_smmu_as *as = to_smmu_as(domain);
> >>> -	struct device_node *np = dev->of_node;
> >>> -	struct of_phandle_args args;
> >>>  	unsigned int index = 0;
> >>>  	int err = 0;
> >>>  
> >>> -	while (!of_parse_phandle_with_args(np, "iommus", "#iommu-cells", index,
> >>> -					   &args)) {
> >>> -		unsigned int swgroup = args.args[0];
> >>> -
> >>> -		if (args.np != smmu->dev->of_node) {
> >>> -			of_node_put(args.np);
> >>> -			continue;
> >>> -		}
> >>> -
> >>> -		of_node_put(args.np);
> >>> +	if (!fwspec || fwspec->ops != &tegra_smmu_ops)
> >>> +		return -ENOENT;
> >>
> >> s/&tegra_smmu_ops/smmu->iommu.ops/
> >>
> >> Secondly, is it even possible that fwspec could be NULL here or that
> >> fwspec->ops != smmu->ops?
> > 
> > I am following what's in the arm-smmu driver, as I think it'd be
> > a common practice to do such a check in such a way.
> > 
> 
> Please check whether it's really needed. It looks like it was needed
> sometime ago, but that's not true anymore.

Given that most iommu drivers have ->ops check, I'd like to
have it also for safety. If someday that's not true anymore,
I'd expect someone to update all existing drivers.