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

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Message-ID: <81491f7e-bd2c-7e3c-14c4-a7547d76c307@linaro.org>
Date:   Mon, 17 Jul 2023 22:19:22 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Bhupesh Sharma <bhupesh.sharma@...aro.org>,
        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,
        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 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.

Konrad
> 
> Thanks,
> Bhupesh