linux-kernel - Re: [PATCHv3 4/6] iommu/arm-smmu-qcom: Request direct mapping for modem device

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Date:   Mon, 20 Apr 2020 23:40:42 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Evan Green <evgreen@...omium.org>
Subject: Re: [PATCHv3 4/6] iommu/arm-smmu-qcom: Request direct mapping for
 modem device

Hi Robin,

On 2020-04-20 22:39, Robin Murphy wrote:
> On 2020-04-20 5:42 pm, Sai Prakash Ranjan wrote:
>> From: Sibi Sankar <sibis@...eaurora.org>
>> 
>> Request direct mapping for modem on platforms which don't have 
>> TrustZone
>> (which programs the modem SIDs) to prevent the following global faults 
>> seen
>> on Cheza/Trogdor:
> 
> Not strictly true - it's patch #6/6 that prevents *those* faults (and
> these days the driver should be reporting unmatched streams a little
> more helpfully). This change would resolve the context faults and/or
> weird memory corruption that might result from applying patch #6 alone
> - this is the crazy thing where transactions sometimes go directly to
> DRAM round the side of the SMMU so we can never safely remap anything,
> right?
> 

True this doesnt prevent global faults, the fault details should go to 
patch6.
I'll update the commit msg something like below:

The Q6 modem sub-system has direct access to DDR through memnoc.
Also SMMU is not expected to provide access control/translation for 
these SIDs
(sandboxing of the modem is achieved through XPUs engaged using SMC 
calls).

Thanks,
Sai

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