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

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Message-ID: <nhthg2rlfatc2pyhsuoulvo5447cxg7buv4aq3r7r5amsmjjoq@pgfyvvegfron>
Date: Sat, 26 Oct 2024 21:18:28 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: 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 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?

-- 
With best wishes
Dmitry