linux-kernel - Re: [PATCH v2 1/8] iommu/amd: Refactor AMD IOMMU debugfs initial setup

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Message-ID: <20241126191228.GA2650296@bhelgaas>
Date: Tue, 26 Nov 2024 13:12:28 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
Cc: joro@...tes.org, suravee.suthikulpanit@....com, will@...nel.org,
	robin.murphy@....com, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, vasant.hegde@....com
Subject: Re: [PATCH v2 1/8] iommu/amd: Refactor AMD IOMMU debugfs initial
 setup

On Wed, Nov 06, 2024 at 01:16:32PM +0530, Dheeraj Kumar Srivastava wrote:
> Rearrange initial setup of AMD IOMMU debugfs to segregate per IOMMU
> setup and setup which is common for all IOMMUs. This ensures that common
> debugfs paths (introduced in subsequent patches) are created only once
> instead of being created for each IOMMU.
> ...

> -void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
> +void amd_iommu_debugfs_setup(void)
>  {
> +	struct amd_iommu *iommu;
>  	char name[MAX_NAME_LEN + 1];
>  
> -	mutex_lock(&amd_iommu_debugfs_lock);
> -	if (!amd_iommu_debugfs)
> -		amd_iommu_debugfs = debugfs_create_dir("amd",
> -						       iommu_debugfs_dir);
> -	mutex_unlock(&amd_iommu_debugfs_lock);
> +	amd_iommu_debugfs = debugfs_create_dir("amd", iommu_debugfs_dir);
>  
> -	snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu->index);
> -	iommu->debugfs = debugfs_create_dir(name, amd_iommu_debugfs);
> +	for_each_iommu(iommu) {
> +		snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu->index);
> +		iommu->debugfs = debugfs_create_dir(name, amd_iommu_debugfs);
> +	}

Doing this setup with for_each_iommu() precludes any hot-add of
IOMMUs, but I guess there's no indication of hotplug support anyway
given all the uses of for_each_iommu() in init_iommu_all(),
amd_iommu_init_pci(), amd_iommu_enable_interrupts(), etc.

>  }
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 43131c3a2172..d78dc96bbec3 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3377,7 +3377,6 @@ int amd_iommu_enable_faulting(unsigned int cpu)
>   */
>  static int __init amd_iommu_init(void)
>  {
> -	struct amd_iommu *iommu;
>  	int ret;
>  
>  	ret = iommu_go_to_state(IOMMU_INITIALIZED);
> @@ -3391,8 +3390,8 @@ static int __init amd_iommu_init(void)
>  	}
>  #endif
>  
> -	for_each_iommu(iommu)
> -		amd_iommu_debugfs_setup(iommu);
> +	if (!ret)
> +		amd_iommu_debugfs_setup();
>  
>  	return ret;
>  }
> -- 
> 2.25.1
>