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

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Message-ID: <8cfddb6cbc424b131c9ab823c0c0f3f1@codeaurora.org>
Date:   Mon, 16 Mar 2020 22:07:04 +0530
From:   Sibi Sankar <sibis@...eaurora.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     bjorn.andersson@...aro.org, robh+dt@...nel.org, joro@...tes.org,
        ohad@...ery.com, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        agross@...nel.org, linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH 0/3] Request direct mapping for modem firmware subdevice

Hey Christoph,
Thanks for taking time to review
the series.

On 2020-03-16 21:20, Christoph Hellwig 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).
> 
> Please fix your device tree so that the device isn't bound to an
> IOMMU.

the bindings proposed in the series
would add a sub-device with an iommu
property.

modem_pil: remoteproc@...xx {
...
    modem-firmware {
         iommus = <&apps_smmu 0x460 0x1>;
    };
...
};

Remoteproc device will not have a iommu
property but modem-firmware sub-device
will.

With ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT y,
we would want to configure the SID either
in direct mapping or bypass (either will
do since protection is achieved through
other means)

https://lore.kernel.org/lkml/497e40b8-300f-1b83-4312-93a58c459d1d@arm.com/

Currently the restructuring is trending
towards whats discussed in the ^^ thread.
i.e either direct mapping/bypass will be
done in the SoC specific corner of the
SMMU driver.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project.