linux-kernel - Re: [PATCH v3 0/3] perf/smmuv3: Don't reserve the PMCG register spaces

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Date:   Thu, 28 Jan 2021 20:31:49 +0000
From:   Will Deacon <will@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Mark Rutland <mark.rutland@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v3 0/3] perf/smmuv3: Don't reserve the PMCG register
 spaces

On Wed, Jan 27, 2021 at 07:32:55PM +0800, Zhen Lei wrote:
> v2 --> v3:
> Patch 3 is updated because https://lkml.org/lkml/2021/1/22/532 has been queued in advance.
> 
> v1 --> v2:
> According to Robin Murphy's suggestion: https://lkml.org/lkml/2021/1/20/470
> Don't reserve the PMCG register spaces, and reserve the entire SMMU register space.
> 
> v1:
> Since the PMCG may implement its resigters space(4KB Page0 and 4KB Page1)
> within the SMMUv3 64KB Page0. In this case, when the SMMUv3 driver reserves the
> 64KB Page0 resource in advance, the PMCG driver try to reserve its Page0 and
> Page1 resources, a resource conflict occurs.
> 
> commit 52f3fab0067d6fa ("iommu/arm-smmu-v3: Don't reserve implementation
> defined register space") reduce the resource reservation range of the SMMUv3
> driver, it only reserves the first 0xe00 bytes in the 64KB Page0, to avoid
> the above-mentioned resource conflicts.
> 
> But the SMMUv3.3 add support for ECMDQ, its registers space is also implemented
> in the SMMUv3 64KB Page0. This means we need to build two separate mappings.
> New features may be added in the future, and more independent mappings may be
> required. The simple problem is complicated because the user expects to map the
> entire SMMUv3 64KB Page0.
> 
> Therefore, the proper solution is: If the PMCG register resources are located in
> the 64KB Page0 of the SMMU, the PMCG driver does not reserve the conflict resources
> when the SMMUv3 driver has reserved the conflict resources before. Instead, the PMCG
> driver only performs devm_ioremap() to ensure that it can work properly.
> 
> Zhen Lei (3):
>   perf/smmuv3: Don't reserve the PMCG register spaces
>   perf/smmuv3: Add a MODULE_SOFTDEP() to indicate dependency on SMMU
>   iommu/arm-smmu-v3: Reserving the entire SMMU register space

I'll need Robin's ack on these.

Will