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

[Svyatoslav Ryhel]

вт, 1 квіт. 2025 р. о 16:34 Artur Kowalski <arturkow2000 at gmail.com> пише:
>
>
> W dniu 31.03.2025 o 07:51, Svyatoslav Ryhel pisze:
> > 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.
> Ok, then I'll drop DTS changes. I will add few words about this option
> in Transformer documentation
> and a note in Kconfig help to not surprise users with not booting U-Boot
> as enabling this option without
> changing DTS causes U-Boot to hang.

You should remove then Kconfig option as well. Add a new chapter to
Transformer T20 documentation which describes this method, here[1] you
may find a similar approach but info is in the commit message of
tegra30 uart-e funcmux. Additionally, as I have said previously, these
changes can be contained in the transformer t20 board file by using
some device tree manipulations from there.

---
1 https://source.denx.de/u-boot/u-boot/-/commit/b515d7ae0de51a26f73b2ddb5ea4db0d95b67d7a