linux-kernel - Re: [RFC PATCH 0/3] Introduce iommu-map-masked for platform devices

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Message-ID: <6gx74wxie4wcabq27wo5y7v36uuurez4jxlzanroepqazdlgtw@sdtv2ld47d3q>
Date: Tue, 14 Oct 2025 21:35:38 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Bryan O'Donoghue <bod@...nel.org>
Cc: Robin Murphy <robin.murphy@....com>,
        Charan Teja Kalla <charan.kalla@....qualcomm.com>, joro@...tes.org,
        will@...nel.org, saravanak@...gle.com, conor+dt@...nel.org,
        robh@...nel.org, mchehab@...nel.org, krzk+dt@...nel.org,
        abhinav.kumar@...ux.dev, vikash.garodia@....qualcomm.com,
        dikshita.agarwal@....qualcomm.com,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        bjorn.andersson@....qualcomm.com, linux-media@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Subject: Re: [RFC PATCH 0/3] Introduce iommu-map-masked for platform devices

On Tue, Oct 14, 2025 at 04:07:37PM +0100, Bryan O'Donoghue wrote:
> On 13/10/2025 13:31, Dmitry Baryshkov wrote:
> > 
> > And from DT perspective compare:
> > 
> > 		fastrpc {
> > 			compatible = "qcom,fastrpc";
> > 			#address-cells = <1>;
> > 			#size-cells = <0>;
> > 
> > 			compute-cb@3 {
> > 				compatible = "qcom,fastrpc-compute-cb";
> > 				reg = <3>;
> > 				iommus = <&apps_smmu 0x1803 0x0>;
> > 			};
> > 
> > 			compute-cb@4 {
> > 				compatible = "qcom,fastrpc-compute-cb";
> > 				reg = <4>;
> > 				iommus = <&apps_smmu 0x1804 0x0>;
> > 			};
> > 
> > 			compute-cb@5 {
> > 				compatible = "qcom,fastrpc-compute-cb";
> > 				reg = <5>;
> > 				iommus = <&apps_smmu 0x1805 0x0>;
> > 			};
> > 		};
> 
> Sorry this is perfect.
> 
> Each function id can be associated with a device and a compat string
> associated with it.

So, which part of the hardware is described by the -cb device? What does
it mean _here_?

> There's no weirdness with iommu-map, you get a struct device for your SID
> and you associate the SID with the FUNCTION_ID you want.
> 
> In fact the FUNCTION_ID could conceivably be the reg. It could be stored in
> platform code.

-- 
With best wishes
Dmitry