linux-kernel - Re: [PATCH 3/4] arm64: dts: qcom: sa8540p-ride: add qup1_i2c15 and qup2

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Date:   Wed, 14 Dec 2022 07:30:13 -0500
From:   Brian Masney <bmasney@...hat.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>, quic_shazhuss@...cinc.com
Cc:     andersson@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        robh+dt@...nel.org, johan+linaro@...nel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, ahalaney@...hat.com,
        echanude@...hat.com
Subject: Re: [PATCH 3/4] arm64: dts: qcom: sa8540p-ride: add qup1_i2c15 and
 qup2_i2c18 nodes

On Tue, Dec 13, 2022 at 03:48:27PM +0100, Konrad Dybcio wrote:
> > +	qup1_i2c15_default: qup1-i2c15-state {
> > +		mux-pins {
> > +			pins = "gpio36", "gpio37";
> > +			function = "qup15";
> > +		};
> > +
> > +		config-pins {
> > +			pins = "gpio36", "gpio37";
> > +			drive-strength = <0x02>;
> > +			bias-pull-up;
> > +		};
> > +	};
>
> You can drop mux/config-pins and have the pin properties live directly
> under the qup1-i2cN-state node.

Hi Konrad (and Shazad below), 

I need to enable 5 i2c buses (0, 1, 12, 15, 18) on this board. I tried
the following combinations with the pin mapping configuration and the
only one that seems to work reliably for me is what I originally had.

With the following, only 2 out of the 5 buses are detected. There's no
i2c mesages in dmesg.

    i2c0_default: i2c0-default-state {
        pins = "gpio135", "gpio136";
        function = "qup15";
    };

Next, I added a drive-strength and bias-pull-up. All 5 buses are
detected. One bus throws read errors when I probe it with i2cdetect, two
others 'i2cdetect -a -y $BUSNUM' takes ~5 seconds to run, and the
remaining two are fast.

    i2c0_default: i2c0-default-state {
        pins = "gpio135", "gpio136";
        function = "qup15";
        drive-strength = <2>;
        bias-pull-up;
    };

This is the style where i2cdetect seems to be happy for all 5 buses and
is fast:

    i2c0_default: i2c0-default-state {
        mux-pins {
            pins = "gpio135", "gpio136";
            function = "qup0";
        };

        config-pins {
            pins = "gpio135", "gpio136";
            drive-strength = <2>;
            bias-pull-up;
        };
    };

Shazad: 'i2cdetect -a -y $BUSNUM) shows that all 5 buses have the same
addresses listening. Is that expected? That seems a bit odd to me.

[root@...alhost ~]# i2cdetect -a -y 0
Warning: Can't use SMBus Quick Write command, will skip some addresses
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                                                 
10:                                                 
20:                                                 
30: -- -- -- -- -- -- -- --                         
40:                                                 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60:                                                 
70:                                                 

I triple checked that I have the QUP pins defined correctly for the 5
buses. I checked them against what's in the downstream kernel and I also
checked them against what's in upstream's
drivers/pinctrl/qcom/pinctrl-sc8280xp.c. This is the pin mapping that I
have:

    i2c0: gpio135, gpio136
    i2c1: gpio158, gpio159
    i2c12: gpio0, gpio1
    i2c15: gpio36, gpio37
    i2c18: gpio66, gpio67

Brian