linux-kernel - Re: [PATCH V5 3/7] arm64: dts: sc7280: Add QUPv3 wrapper

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Date:   Wed, 01 Sep 2021 12:36:57 +0530
From:   rajpat@...eaurora.org
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, swboyd@...omium.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, rnayak@...eaurora.org,
        saiprakash.ranjan@...eaurora.org, msavaliy@....qualcomm.com,
        skakit@...eaurora.org, dianders@...omium.org
Subject: Re: [PATCH V5 3/7] arm64: dts: sc7280: Add QUPv3 wrapper_0 nodes

On 2021-08-27 01:21, Matthias Kaehlcke wrote:
> On Thu, Aug 26, 2021 at 06:37:02PM +0530, rajpat@...eaurora.org wrote:
>> On 2021-08-12 19:44, Matthias Kaehlcke wrote:
>> > On Thu, Aug 12, 2021 at 01:11:14PM +0530, Rajesh Patil wrote:
>> > > From: Roja Rani Yarubandi <rojay@...eaurora.org>
>> > >
>> > > Add QUPv3 wrapper_0 DT nodes for SC7280 SoC.
>> > >
>> > > Signed-off-by: Roja Rani Yarubandi <rojay@...eaurora.org>
>> > > Signed-off-by: Rajesh Patil <rajpat@...eaurora.org>
>> > > ---
>> > >  arch/arm64/boot/dts/qcom/sc7280.dtsi | 720
>> > > +++++++++++++++++++++++++++++++++++
>> > >  1 file changed, 720 insertions(+)
>> > >
>> > > diff --git a/arch/arm64/boot/dts/qcom/sc7280.dtsi
>> > > b/arch/arm64/boot/dts/qcom/sc7280.dtsi
>> > > index f8dd5ff..e461395 100644
>> > > --- a/arch/arm64/boot/dts/qcom/sc7280.dtsi
>> > > +++ b/arch/arm64/boot/dts/qcom/sc7280.dtsi
>> > >
>> > > ...
>> > >
>> > > +			spi0: spi@...000 {
>> > > +				compatible = "qcom,geni-spi";
>> > > +				reg = <0 0x00980000 0 0x4000>;
>> > > +				clock-names = "se";
>> > > +				clocks = <&gcc GCC_QUPV3_WRAP0_S0_CLK>;
>> > > +				pinctrl-names = "default";
>> > > +				pinctrl-0 = <&qup_spi0_data_clk>, <&qup_spi0_cs>,
>> > > <&qup_spi0_cs_gpio>;
>> >
>> > What is the story behind 'qup_spiN_cs' and 'qup_spiN_cs_gpio'? Both
>> > configure
>> > the CS pin with a different function:
>> >
>> 
>> As per discussion here [1], we have split like this.
>> 
>> [1] https://lore.kernel.org/patchwork/patch/1393353/#1591826
> 
> IIUC that's only about having separate configs for each pin, instead of
> groups like 'qup-spi0-default'. What you are doing above with 
> 'qup_spi0_cs'
> and 'qup_spi0_cs_gpio' is to configure the same pin (GPIO 3) both as 
> SPI
> chip select and as GPIO. Which one is it?
> 
> I imagine we want to have both pinctrl definitions to allow a board to
> configure the pin either as SPI CS or GPIO. However it should be only 
> one
> of the two at a time, and the SoC .dtsi should provide a reasonable
> default, which probably is SPI CS.
> 

I agree. Will remove it in next version.

> Maybe I'm missing something, if so please provide details on why it is
> necessary to have this config.