linux-kernel - Re: [PATCH 1/5] iommu/tegra-smmu: Unwrap tegra_smmu_group

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Message-ID: <20200928071356.GD2837573@ulmo>
Date:   Mon, 28 Sep 2020 09:13:56 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     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 1/5] iommu/tegra-smmu: Unwrap tegra_smmu_group_get

On Sat, Sep 26, 2020 at 01:07:15AM -0700, Nicolin Chen wrote:
> The tegra_smmu_group_get was added to group devices in different
> SWGROUPs and it'd return a NULL group pointer upon a mismatch at
> tegra_smmu_find_group(), so for most of clients/devices, it very
> likely would mismatch and need a fallback generic_device_group().
> 
> But now tegra_smmu_group_get handles devices in same SWGROUP too,
> which means that it would allocate a group for every new SWGROUP
> or would directly return an existing one upon matching a SWGROUP,
> i.e. any device will go through this function.
> 
> So possibility of having a NULL group pointer in device_group()
> is upon failure of either devm_kzalloc() or iommu_group_alloc().
> In either case, calling generic_device_group() no longer makes a
> sense. Especially for devm_kzalloc() failing case, it'd cause a
> problem if it fails at devm_kzalloc() yet succeeds at a fallback
> generic_device_group(), because it does not create a group->list
> for other devices to match.
> 
> This patch simply unwraps the function to clean it up.
> 
> Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
> ---
>  drivers/iommu/tegra-smmu.c | 19 ++++---------------
>  1 file changed, 4 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> index 0becdbfea306..6335285dc373 100644
> --- a/drivers/iommu/tegra-smmu.c
> +++ b/drivers/iommu/tegra-smmu.c
> @@ -903,11 +903,13 @@ static void tegra_smmu_group_release(void *iommu_data)
>  	mutex_unlock(&smmu->lock);
>  }
>  
> -static struct iommu_group *tegra_smmu_group_get(struct tegra_smmu *smmu,
> -						unsigned int swgroup)
> +static struct iommu_group *tegra_smmu_device_group(struct device *dev)
>  {
> +	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> +	struct tegra_smmu *smmu = dev_iommu_priv_get(dev);
>  	const struct tegra_smmu_group_soc *soc;
>  	struct tegra_smmu_group *group;
> +	int swgroup = fwspec->ids[0];

This should be unsigned int to match the type of swgroup elsewhere.
Also, it might not be worth having an extra local variable for this
since it's only used once.

Thierry

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