linux-kernel - Re: [PATCH v3 4/4] arm64: dts: qcom: qcs615: add the APPS SMMU node

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Message-ID: <828c465f-684b-4257-86cb-d9c753fc30f1@oss.qualcomm.com>
Date: Mon, 28 Oct 2024 16:46:34 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Qingqing Zhou <quic_qqzhou@...cinc.com>, andersson@...nel.org,
        konradybcio@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
        conor+dt@...nel.org, robimarko@...il.com, will@...nel.org,
        robin.murphy@....com, joro@...tes.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux.dev
Subject: Re: [PATCH v3 4/4] arm64: dts: qcom: qcs615: add the APPS SMMU node

On 26.10.2024 8:18 PM, Dmitry Baryshkov wrote:
> On Fri, Oct 25, 2024 at 06:45:01PM +0200, Konrad Dybcio wrote:
>> On 25.10.2024 1:06 PM, Dmitry Baryshkov wrote:
>>> On Fri, Oct 25, 2024 at 10:54:24AM +0200, Konrad Dybcio wrote:
>>>> On 25.10.2024 5:07 AM, Qingqing Zhou wrote:
>>>>> Add the APPS SMMU node for QCS615 platform. Add the dma-ranges
>>>>> to limit DMA address range to 36bit width to align with system
>>>>> architecture.
>>>>>
>>>>> Signed-off-by: Qingqing Zhou <quic_qqzhou@...cinc.com>
>>>>> ---
>>>>
>>>> You probably also want to mark it `dma-coherent` (see e.g.
>>>> x1e80100.dtsi)
>>>
>>> Is it? I don't think SM6150 had dma-coherent SMMU, at least it wasn't
>>> marked as such.
>>
>> I don't think I have any documentation on this, so.. one way to find out!
> 
> I don't have qcs615 at hand, so a purely theoretical question. But how
> should it break if we mark it as dma-coherent, while it is not?

The board will hang rather quickly

Konrad