[PATCH v2 3/3] tegra: allow to expose UART on microSD slot

[Svyatoslav Ryhel]

нд, 30 бер. 2025 р. о 22:27 Artur Kowalski <arturkow2000 at gmail.com> пише:
>
> Tegra20 has mux allowing to repurpose microSD as UART on boards which
> use sdmmc3 controller for microSD. Add TEGRA_UARTA_MICROSD to enable
> this feature. It is currently supported on Transformer T20, support for
> other boards may require Device Tree changes.
>
> Update Transformer T20 DTS to select correct pinmux and stdout-path
> based on TEGRA_UARTA_MICROSD.
>
> Signed-off-by: Artur Kowalski <arturkow2000 at gmail.com>
> ---
>
> Changes in v2:
> - added TEGRA_UARTA_MICROSD Kconfig option
> - removed .dtsi for enabling UART over microSD
> - modified transformer DT to use UARTA and correct pinmux when
>   TEGRA_UARTA_MICROSD is enabled; it is enough to flip a single
>   switch to enable/disable UART over microSD
>
>  arch/arm/dts/tegra20-asus-transformer.dtsi | 24 ++++++++++++++++++++++
>  arch/arm/mach-tegra/tegra20/Kconfig        | 15 ++++++++++++++
>  2 files changed, 39 insertions(+)
>
> diff --git a/arch/arm/dts/tegra20-asus-transformer.dtsi b/arch/arm/dts/tegra20-asus-transformer.dtsi
> index 49efabbfd92..9ea323c81f3 100644
> --- a/arch/arm/dts/tegra20-asus-transformer.dtsi
> +++ b/arch/arm/dts/tegra20-asus-transformer.dtsi
> @@ -5,7 +5,13 @@
>
>  / {
>         chosen {
> +#if CONFIG_IS_ENABLED(TEGRA_ENABLE_UARTA)
> +               stdout-path = &uarta;
> +#elif CONFIG_IS_ENABLED(TEGRA_ENABLE_UARTD)
>                 stdout-path = &uartd;
> +#else
> +#error Unsupported UART
> +#endif
>         };
>
>         aliases {
> @@ -195,10 +201,17 @@
>                                 nvidia,function = "i2c1";
>                         };
>
> +#if CONFIG_IS_ENABLED(TEGRA_UARTA_SDB_SDD)
> +                       dbguart {
> +                               nvidia,pins = "sdb", "sdd";
> +                               nvidia,function = "uarta";
> +                       };
> +#else
>                         sdb {
>                                 nvidia,pins = "sdb", "sdc", "sdd", "slxc", "slxk";
>                                 nvidia,function = "sdio3";
>                         };
> +#endif
>
>                         sdio1 {
>                                 nvidia,pins = "sdio1";
> @@ -376,7 +389,13 @@
>                 };
>         };
>
> +#if CONFIG_IS_ENABLED(TEGRA_ENABLE_UARTA)
> +       uarta: serial at 70006000 {
> +#elif CONFIG_IS_ENABLED(TEGRA_ENABLE_UARTD)
>         uartd: serial at 70006300 {
> +#else
> +#error Unsupported UART
> +#endif
>                 status = "okay";
>                 clock-frequency = <216000000>;
>         };
> @@ -434,7 +453,12 @@
>         };
>
>         sdmmc3: sdhci at c8000400 {
> +#if CONFIG_IS_ENABLED(TEGRA_UARTA_MICROSD)
> +               /* Can't use both at the same time */
> +               status = "disabled";
> +#else
>                 status = "okay";
> +#endif
>                 bus-width = <4>;
>
>                 cd-gpios = <&gpio TEGRA_GPIO(I, 5) GPIO_ACTIVE_LOW>;
> diff --git a/arch/arm/mach-tegra/tegra20/Kconfig b/arch/arm/mach-tegra/tegra20/Kconfig
> index 3349f1e2786..c2c51660216 100644
> --- a/arch/arm/mach-tegra/tegra20/Kconfig
> +++ b/arch/arm/mach-tegra/tegra20/Kconfig
> @@ -77,6 +77,21 @@ endchoice
>  config SYS_SOC
>         default "tegra20"
>
> +config TEGRA_UARTA_MICROSD
> +       bool "UARTA on MicroSD breakout board"
> +       default n
> +       depends on TEGRA_ENABLE_UARTA && TARGET_TRANSFORMER_T20
> +       select TEGRA_UARTA_SDB_SDD
> +       help
> +         Repurpose the SD card slot for getting access to the UARTA serial
> +         console. Primarily useful only for low level u-boot debugging on
> +         tablets, where normal UARTD is difficult to access and requires
> +         device disassembly and/or soldering. Enabling this option causes
> +         UARTA TX to become exposed on SDD and RX on SDB pins which correspond
> +         to microSD CLK and CMD pins respectively. Currently this is supported
> +         only on Transformer T20, support for other platforms may require DT
> +         and configs (from include/configs/*) updates.
> +
>  source "board/nvidia/harmony/Kconfig"
>  source "board/avionic-design/medcom-wide/Kconfig"
>  source "board/compal/paz00/Kconfig"
> --
> 2.48.1
>

This is not applicable since this is a hack by nature, BUT if you
contain this in the transformer t20 board and Kconfig (no dts
changes), this may be applied.