linux-kernel - Re: [PATCH v4 1/3] iommu/tegra-smmu: Use fwspec in tegra_smmu_(de)attach

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Message-ID: <e594374b-d701-fb6f-93f2-4efb9c5eb608@gmail.com>
Date:   Fri, 2 Oct 2020 23:12:18 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     thierry.reding@...il.com, joro@...tes.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 v4 1/3] iommu/tegra-smmu: Use fwspec in
 tegra_smmu_(de)attach_dev

02.10.2020 22:45, Nicolin Chen пишет:
> On Fri, Oct 02, 2020 at 05:41:50PM +0300, Dmitry Osipenko wrote:
>> 02.10.2020 09:08, 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)
>>> +		return -ENOENT;
>>
>> Could the !fwspec ever be true here as well?
> 
> There are multiple callers of this function. It's really not that
> straightforward to track every one of them. So I'd rather have it
> here as other iommu drivers do. We are human beings, so we could
> have missed something somewhere, especially callers are not from
> tegra-* drivers.
> 

I'm looking at the IOMMU core and it requires device to be in IOMMU
group before attach_dev() could be called.

The group can't be assigned to device without the fwspec, see
tegra_smmu_device_group().

Seems majority of IOMMU drivers are checking dev_iommu_priv_get() for
NULL in attach_dev(), some not checking anything, some check both and
only arm-smmu checks the fwspec.