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

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Message-ID: <CAH=2NtxX9jC6-7=bWEWTtgO=5VqX5U_ngnC6vWFZxDJUdsdg+g@mail.gmail.com>
Date:   Tue, 18 Jul 2023 01:52:44 +0530
From:   Bhupesh Sharma <bhupesh.sharma@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Stephan Gerhold <stephan@...hold.net>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-usb@...r.kernel.org, agross@...nel.org, andersson@...nel.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 Tue, 18 Jul 2023 at 01:49, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>
> On 17.07.2023 22:09, Bhupesh Sharma wrote:
> > On Mon, 17 Jul 2023 at 23:58, Stephan Gerhold <stephan@...hold.net> wrote:
> >>
> >> On Mon, Jul 17, 2023 at 11:33:40PM +0530, Bhupesh Sharma wrote:
> >>> 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.
> >>>
> >>
> >> IMO a vendor-specific DT property is still better than messing up the
> >> device separation in the device tree. The same "tcsr-base" reg would
> >> also appear on the actual tcsr syscon device tree node. Having two
> >> device tree nodes with the same reg region is generally not valid.
> >>
> >> Something like qcom,eud-sec-reg = <&tcsr_reg yyyy> would at least make
> >> clear that this points into a region that is shared between multiple
> >> different devices, while adding it as reg suggests that TCSR belongs
> >> exclusively to EUD.
> >
> > I understand your point but since for sm6115 / qcm2290 devices TCSR is
> > not used for any other purpose than EUD, I still think introducing a
> > new soc / vendor specific dt-property might be an overkill for this
> > changeset.
> Untrue, there's some mumblings around the PHY properties and PSHOLD.
> I think Stephan may be correct here.

Can you share the links to those discussions?

Thanks,
Bhupesh