linux-kernel - Re: [RFC v12 13/13] iommu/arm-smmu: Add a init_context

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Message-ID: <20200813130342.GA10256@willie-the-truck>
Date:   Thu, 13 Aug 2020 14:03:43 +0100
From:   Will Deacon <will@...nel.org>
To:     Jordan Crouse <jcrouse@...eaurora.org>
Cc:     linux-arm-msm@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        iommu@...ts.linux-foundation.org, freedreno@...ts.freedesktop.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Krishna Reddy <vdumpa@...dia.com>,
        Pritesh Raithatha <praithatha@...dia.com>,
        Sibi Sankar <sibis@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Thierry Reding <treding@...dia.com>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v12 13/13] iommu/arm-smmu: Add a init_context_bank
 implementation hook

On Mon, Aug 10, 2020 at 04:26:57PM -0600, Jordan Crouse wrote:
> Add a new implementation hook to allow the implementation specific code
> to tweek the context bank configuration just before it gets written.
> The first user will be the Adreno GPU implementation to turn on
> SCTLR.HUPCF to ensure that a page fault doesn't terminating pending
> transactions. Doing so could hang the GPU if one of the terminated
> transactions is a CP read.
> 
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
> 
>  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 16 ++++++++++++++++
>  drivers/iommu/arm/arm-smmu/arm-smmu.c      | 21 +++++++++++++--------
>  drivers/iommu/arm/arm-smmu/arm-smmu.h      |  5 +++++
>  3 files changed, 34 insertions(+), 8 deletions(-)

We already have ->init_context(), so I'd prefer to use that instead of
adding another callback. Could we stick a couple of fields in
smmu_domain->cfg (e.g. sctlr_set, sctlr_clr) and handle those a bit like
we do for the asid/vmid on cavium implementations?

Will