[PATCH] arm: mvebu: x240: Use i2c-gpio instead of built in controller

[Chris Packham]

Hi Me,

On Thu, Jul 20, 2023 at 3:03 PM Chris Packham <judge.packham at gmail.com> wrote:
>
> There is an Errata with the built-in I2C controller where various I2C
> hardware errors cause a complete lockup of the CPU (which eventually
> results in an watchdog reset).
>
> Put the I2C MPP pins into GPIO mode and use the i2c-gpio driver instead.
> This uses a bit-banged implementation of an I2C controller and avoids
> triggering the Errata.
>
> Signed-off-by: Chris Packham <judge.packham at gmail.com>
> ---
> This is dependent on a bug-fix for the i2c-gpio driver I just sent
> out[1] (sorry I should have sent them as a series but I thought this
> would take me longer to test than it did).
>
> [1] - https://lore.kernel.org/u-boot/20230720023107.1184147-1-judge.packham@gmail.com/
>
>  arch/arm/dts/ac5-98dx35xx-atl-x240.dts | 30 ++++++++++++++++++++++----
>  configs/x240_defconfig                 |  1 +
>  2 files changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/dts/ac5-98dx35xx-atl-x240.dts b/arch/arm/dts/ac5-98dx35xx-atl-x240.dts
> index 820ec18b4355..d47220520b9e 100644
> --- a/arch/arm/dts/ac5-98dx35xx-atl-x240.dts
> +++ b/arch/arm/dts/ac5-98dx35xx-atl-x240.dts
> @@ -71,8 +71,25 @@
>  };
>
>  &i2c0 {
> -       status = "okay";
> +       status = "disabled";
> +};

I'll remove this section completely. I did want to make it clear that
we're using the same pins just as GPIOs instead of the dedicated I2C
mode which has issues but that can be explained better in the commit
message.

>
> +&{/} {

I should probably move this part up to the root node rather than
addressing it here.

> +       i2cgpio: i2c-gpio-0 {
> +                       compatible = "i2c-gpio";
> +                       #address-cells = <1>;
> +                       #size-cells = <0>;
> +
> +                       pinctrl-names = "default";
> +                       pinctrl-0 =  <&i2c0_gpio>;
> +                       scl-gpios = <&gpio0 26 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
> +                       sda-gpios = <&gpio0 27 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
> +                       i2c-gpio,delay-us = <2>;
> +                       status = "okay";
> +                };
> +};
> +
> +&i2cgpio {
>         mux at 71 {
>                 #address-cells = <1>;
>                 #size-cells = <0>;
> @@ -177,8 +194,8 @@
>          * LED_OE_N              [23]
>          * USB_PWR_FLT_N         [24]
>          * SFP_INT_N             [25]
> -        * I2C0_SCL              [26]
> -        * I2C0_SDA              [27]
> +        * I2C0_SCL              [26] (GPIO)
> +        * I2C0_SDA              [27] (GPIO)
>          * USB_EN                [28]
>          * MONITOR_INT_N         [29]
>          * XM1_MDC               [30]
> @@ -201,7 +218,7 @@
>         /*           0    1    2    3    4    5    6    7    8    9 */
>         pin-func = < 0xff 0xff 0xff 0xff 0xff 0xff 0xff 0xff 0xff 0xff
>                      0xff 0xff 1    1    1    1    0xff 0xff 0    0
> -                    0    0    0    0    0    0    1    1    0    0
> +                    0    0    0    0    0    0    0xff 0xff 0    0
>                      1    1    1    1    0    0    0    0    0    0
>                      0    0    0    1    1    1    >;
>
> @@ -209,4 +226,9 @@
>                 marvell,pins = <0 1 2 3 4 5 6 7 8 9 10 11 16 17>;
>                 marvell,function = <2>;
>         };
> +
> +       i2c0_gpio: i2c0-gpio-pins {
> +               marvell,pins = <26 27>;
> +               marvell,function = <0>;
> +       };
>  };
> diff --git a/configs/x240_defconfig b/configs/x240_defconfig
> index 6d25c5ae3fcf..e8589d636081 100644
> --- a/configs/x240_defconfig
> +++ b/configs/x240_defconfig
> @@ -43,6 +43,7 @@ CONFIG_CLK_MVEBU=y
>  CONFIG_GPIO_HOG=y
>  CONFIG_DM_PCA953X=y
>  CONFIG_DM_I2C=y
> +CONFIG_DM_I2C_GPIO=y
>  CONFIG_SYS_I2C_MVTWSI=y
>  CONFIG_I2C_MUX=y
>  CONFIG_I2C_MUX_PCA954x=y
> --
> 2.41.0
>