linux-kernel - Re: [PATCH v8 3/4] arm64: dts: qcom: sm6115: Add EUD dt node and dwc3 connector

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Date:   Mon, 17 Jul 2023 23:33:40 +0530
From:   Bhupesh Sharma <bhupesh.sharma@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-usb@...r.kernel.org, agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...aro.org, linux-kernel@...r.kernel.org,
        bhupesh.linux@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, krzysztof.kozlowski@...aro.org,
        quic_schowdhu@...cinc.com, gregkh@...uxfoundation.org
Subject: Re: [PATCH v8 3/4] arm64: dts: qcom: sm6115: Add EUD dt node and dwc3 connector

On Mon, 17 Jul 2023 at 16:15, Stephan Gerhold <stephan@...hold.net> wrote:
>
> On Mon, Jul 17, 2023 at 04:02:35PM +0530, Bhupesh Sharma wrote:
> > Add the Embedded USB Debugger(EUD) device tree node for
> > SM6115 / SM4250 SoC.
> >
> > The node contains EUD base register region, EUD mode manager
> > register region and TCSR Base register region along with the
> > interrupt entry.
> >
> > [...]
> >
> > Reviewed-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> > Signed-off-by: Bhupesh Sharma <bhupesh.sharma@...aro.org>
> > ---
> >  arch/arm64/boot/dts/qcom/sm6115.dtsi | 50 ++++++++++++++++++++++++++++
> >  1 file changed, 50 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/sm6115.dtsi b/arch/arm64/boot/dts/qcom/sm6115.dtsi
> > index 839c603512403..db45337c1082c 100644
> > --- a/arch/arm64/boot/dts/qcom/sm6115.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/sm6115.dtsi
> > [...]
> > @@ -789,6 +801,37 @@ gcc: clock-controller@...0000 {
> >                       #power-domain-cells = <1>;
> >               };
> >
> > +             eud: eud@...0000 {
> > +                     compatible = "qcom,sm6115-eud", "qcom,eud";
> > +                     reg = <0x0 0x01610000 0x0 0x2000>,
> > +                           <0x0 0x01612000 0x0 0x1000>,
> > +                           <0x0 0x003c0000 0x0 0x40000>;
> > +                     reg-names = "eud-base", "eud-mode-mgr", "tcsr-base";
>
> TCSR is a separate hardware block unrelated to the EUD. IMHO it
> shouldn't be listed as "reg" here.
>
> Typically we describe it as syscon and then reference it from other
> nodes. See e.g. sm8450.dtsi "tcsr: syscon@...0000" referenced in &scm
> "qcom,dload-mode = <&tcsr 0x13000>". This is pretty much exactly the
> same use case as you have. It also uses this to write something with
> qcom_scm_io_writel() at the end.

That was discussed a bit during v1 patchset review. Basically, if we
use a tcsr syscon approach here, we will need to define a 'qcom,xx'
vendor specific dt-property and use something like this in the eud
node:

qcom,eud-sec-reg = <&tcsr_reg yyyy>

which would be then used by the eud driver (via
syscon_regmap_lookup_by_phandle()).

But for sm6115 / qcm2290 this would be an over complicated solution as
normally the eud driver (say sc7280) doesn't need tcsr based secure
mode manager access. So defining a new soc / vendor specific
dt-property might be an overkill.

Thanks,
Bhupesh