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

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Message-ID: <ff805c5c647326c5edaddf2efec5cb87@codeaurora.org>
Date:   Thu, 12 Mar 2020 11:58:30 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Joerg Roedel <joro@...tes.org>, Sibi Sankar <sibis@...eaurora.org>,
        ohad@...ery.com, devicetree@...r.kernel.org,
        linux-kernel-owner@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        bjorn.andersson@...aro.org, iommu@...ts.linux-foundation.org,
        robh+dt@...nel.org, agross@...nel.org,
        saiprakash.ranjan@...eaurora.org
Subject: Re: [PATCH 0/3] Request direct mapping for modem firmware subdevice

Hi Robin,

On 2020-03-10 22:14, Robin Murphy wrote:
> On 10/03/2020 4:23 pm, Joerg Roedel wrote:
>> On Tue, Mar 10, 2020 at 07:30:50PM +0530, Sibi Sankar wrote:
>>> 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).
>> 
>> Okay, this sounds like a case for arm_smmu_get_resv_region(). It 
>> should
>> return an entry for the reserved memory region the firmware needs to
>> access, so that generic iommu can setup this mapping.
>> 
>> Note that it should return that entry only for your device, not for 
>> all
>> devices. Maybe there is a property in DT or IORT you can set to
>> transport this information into the arm-smmu driver.
>> 
>> This is pretty similar to RMRR mapping on the Intel VT-d IOMMU or
>> Unity-mapped ranges in the AMD-Vi IOMMU.
> 
> Yup, a way to describe boot-time memory regions in IORT is in the
> process of being specced out; the first attempt at an equivalent for
> DT is here:
> 
> https://lore.kernel.org/linux-iommu/20191209150748.2471814-1-thierry.reding@gmail.com/
> 
> If that's not enough and the SMMU still needs to treat certain Stream
> IDs specially because they may be untranslatable (due to having direct
> access to memory as a side-channel), then that should be handled in
> the SoC-specific corner of the SMMU driver, not delegated to
> individual endpoint drivers.
> 

Are you talking about this one for SoC specific change - 
https://lore.kernel.org/patchwork/patch/1183530/

Thanks,
Sai

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