linux-kernel - Re: [PATCH v9 5/8] perf/amd/iommu: Modify functions to query max banks and counters

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Message-ID: <20170208193140.pzljikzicjaix6vw@pd.tnic>
Date:   Wed, 8 Feb 2017 20:31:40 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        peterz@...radead.org, joro@...tes.org, mingo@...hat.com
Subject: Re: [PATCH v9 5/8] perf/amd/iommu: Modify functions to query max
 banks and counters

On Tue, Feb 07, 2017 at 02:40:33AM -0600, Suravee Suthikulpanit wrote:
> Currently, amd_iommu_pc_get_max_[banks|counters]() use end-point
> device ID to locate an IOMMU and check the reported max banks/counters.
> The logic assumes that the IOMMU_BASE_DEVID belongs to the first IOMMU,
> and uses it to acquire a reference to the first IOMMU, which does not work
> on certain systems. Instead, modify the function to take an IOMMU index,
> and use it to query the corresponding AMD IOMMU instance.
> 
> Currently, hardcodes the IOMMU index to 0 since the current AMD IOMMU
> perf implementation only supports a single IOMMU. A subsequent
> patch will add support for multiple IOMMUs, and will use a proper IOMMU index.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Joerg Roedel <joro@...tes.org>
> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> ---

...

> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> index 1b5adb4..eb654e7 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -2715,6 +2715,21 @@ bool amd_iommu_v2_supported(void)
>  }
>  EXPORT_SYMBOL(amd_iommu_v2_supported);
>  
> +struct amd_iommu *get_amd_iommu(unsigned int idx)
> +{
> +	unsigned int i = 0;
> +	struct amd_iommu *iommu, *ret = NULL;
> +
> +	for_each_iommu(iommu) {
> +		if (i++ == idx) {
> +			ret = iommu;
> +			break;

			return iommu;

no need for the assignment and the break.

> +		}
> +	}
> +	return ret;
> +}
> +EXPORT_SYMBOL(get_amd_iommu);

-- 
Regards/Gruss,
    Boris.

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