linux-kernel - Re: [PATCH v2 5/8] dt-bindings: misc: add property to support non-secure DSP

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Message-ID: <YbdIas4QE1z7alAc@gerhold.net>
Date:   Mon, 13 Dec 2021 14:19:38 +0100
From:   Stephan Gerhold <stephan@...hold.net>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     robh+dt@...nel.org, gregkh@...uxfoundation.org,
        devicetree@...r.kernel.org, ekangupt@....qualcomm.com,
        jeyr@...eaurora.org, bkumar@....qualcomm.com,
        linux-kernel@...r.kernel.org, bjorn.andersson@...aro.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 5/8] dt-bindings: misc: add property to support
 non-secure DSP

On Mon, Dec 13, 2021 at 12:35:40PM +0000, Srinivas Kandagatla wrote:
> On 13/12/2021 10:57, Stephan Gerhold wrote:
> > On Thu, Dec 09, 2021 at 12:06:23PM +0000, Srinivas Kandagatla wrote:
> > > From: Jeya R <jeyr@...eaurora.org>
> > > 
> > > Add property to set DSP domain as non-secure.
> > > 
> > > ADSP/MDSP/SDSP are by default secured, where as CDSP can be either be
> > > secured/unsecured.
> > 
> > Wouldn't it be easier to avoid the negation and add a "qcom,secure-domain"
> > property instead? Given PATCH 8/8 ("arm64: dts: qcom: add non-secure
> > domain property to fastrpc nodes") it looks like you are intentionally
> > breaking DT compatibility here, but this patch does not justify why this
> > is necessary.
> 
> By default all ADSP/MDSP/SDSP are secured, so this property is only required
> for something that is not default. Only case that is configurable is the
> CDSP case where in by adding this flag we should be able to load an unsigned
> process to dsp using unsecured node.
> 
> Having said that, TBH When we first added the fastrpc patchset we did not
> take care of this security feature properly :-)
> 
> From security point of view, its better to keep the default as secured
> rather than unsecured in DT too.
> 
> With this DTS patch older dts should continue to work.
> 

Is this a "default" on newer platforms only? Why do the existing
platforms not use the "secure" setup then? Or is this perhaps firmware
version/configuration specific?

Basically I'm confused because you say that the "default" is the secured
setup, but DT patch (8/8) suggests that non-secure is the default on
pretty much all currently supported platforms (msm8916, sdm845, sm8150,
sm8250, sm8350). :)

Thanks,
Stephan