linux-kernel - Re: [PATCH v6] iommu/arm-smmu-qcom: Request direct mapping for modem device

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Date:   Mon, 11 May 2020 12:37:09 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Sibi Sankar <sibis@...eaurora.org>, joro@...tes.org,
        robin.murphy@....com, will@...nel.org
Cc:     bjorn.andersson@...aro.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, dianders@...omium.org,
        evgreen@...omium.org, mka@...omium.org,
        Sibi Sankar <sibis@...eaurora.org>
Subject: Re: [PATCH v6] iommu/arm-smmu-qcom: Request direct mapping for modem device

Quoting Sibi Sankar (2020-05-11 10:55:32)
> The modem remote processor has two access paths to DDR. One path is
> directly connected to DDR and another path goes through an SMMU. The
> SMMU path is configured to be a direct mapping because it's used by
> various peripherals in the modem subsystem. Typically this direct
> mapping is configured statically at EL2 by QHEE (Qualcomm's Hypervisor
> Execution Environment) before the kernel is entered.
> 
> In certain firmware configuration, especially when the kernel is already
> in full control of the SMMU, defer programming the modem SIDs to the
> kernel. Let's add compatibles here so that we can have the kernel
> program the SIDs for the modem in these cases.
> 
> Signed-off-by: Sibi Sankar <sibis@...eaurora.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@...omium.org>