linux-kernel - Re: [PATCH 0/3] Request direct mapping for modem firmware subdevice

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Message-ID: <4ed6ddd667a3e6f670084a443d141474@codeaurora.org>
Date:   Tue, 10 Mar 2020 19:30:50 +0530
From:   Sibi Sankar <sibis@...eaurora.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     bjorn.andersson@...aro.org, robh+dt@...nel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-remoteproc@...r.kernel.org, ohad@...ery.com,
        agross@...nel.org, linux-kernel-owner@...r.kernel.org
Subject: Re: [PATCH 0/3] Request direct mapping for modem firmware subdevice

Hey Joerg,
Thanks for taking time to review
the series!

On 2020-03-10 16:53, Joerg Roedel wrote:
> On Mon, Mar 09, 2020 at 11:52:52PM +0530, Sibi Sankar wrote:
>> The Q6 modem sub-system has direct access to DDR through memnoc and
>> an indirect access routed through a SMMU which MSS CE (crypto engine
>> sub-component of MSS) uses during out of reset sequence. Request 
>> direct
>> mapping for the modem-firmware subdevice since smmu is not expected
>> to provide access control/translation for these SIDs (sandboxing of 
>> the
>> modem is achieved through XPUs engaged using SMC calls).
> 
> So the DMA accesses are initiated by the firmware and need to be direct
> mapped? Which memory region do they access?

The accesses are initiated by the firmware
and they access modem reserved regions.
However as explained in ^^ any accesses
outside the region will result in a violation
and is controlled through XPUs (protection units).

With ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT y
the firmware SIDs will explicitly need to
be directly mapped to avoid observing
global faults in the absence of secure
firmware (TrustZone) programming the modem
SIDs as S2CR-Bypass.

> 
> Regards,
> 
> 	Joerg

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