[PATCH 0/4] Support UART over MicroSD slot on Transformer T20

[Artur Kowalski]

Hello

Thanks for quick response. I know UARTD is the dedicated UART for 
debugging on TF101, but exposing UART over microSD
is a handy trick useful for development. As I'm doing development on 
this tablet (bringing U-Boot's UEFI support and latest
Linux), and also still using the device on old OS I'd like to avoid 
disassembling and reassembling it over and over again.
Others too may find the feature useful e. g. to avoid having to solder 
which requires specialized equipment, skills and
is potentially dangerous for the board. Also, there already seems to be 
support for that on Sunxi platforms through
CONFIG_UART0_PORT_F.

Apart from pinmux changes, would it be acceptable to include an option 
to allow switching UARTA mux to
SDB/SDD (currently this has to be selected from board's Kconfig file). 
Doing so would allow to enable UART
over microSD without patching U-Boot's source without changing any 
existing configuration. Then I would
keep DTS overlays and config changes local.

Also, today, after running U-Boot with debug enabled, I discovered some 
failed assertions in pinmux code probably
caused by my changes, I will get that fixed before sending v2.

Best regards
Artur Kowalski

W dniu 18.03.2025 o 09:54, Svyatoslav Ryhel pisze:
> вт, 18 бер. 2025 р. о 10:31 Artur Kowalski <arturkow2000 at gmail.com> пише:
>>
>> The first patch in the series brings general pinmux support for exposing
>> UART over SDB/SDD pins on T20. The following patches bring support
>> Transformer T20 allowing to enable UART over uSD by setting
>>
>> CONFIG_TEGRA_ENABLE_UARTA=y
>> CONFIG_DEVICE_TREE_INCLUDES="tegra20-asus-transformer-uart-usd.dtsi"
>>
>> Similarily, support for UART over uSD could be brought to Ventana which
>> has uSD on the same pins as TF101, and other Ventana-based boards.
>>
> Hey there, thank you for looking into U-Boot for Tegra. If something I
> will say hurts or offends you, I am sorry it was not intentional.
>
> Anyway, apart funcmux changes, all other changes you propose are
> redundant. Asus dedicated uart for logging and console is UARTD any
> other uart configuration must not be added since it will disrupt
> existing configuration. If you need uart and cannot resolve an issue
> without it you can always solder to uart-d or locally mux sd to uart
> console fix your issue and remove it. Uart is not intended way to
> interact with Asus TF101 and doesn't need to be exposed, panel and
> fastboot console are and can be used to resolve most of issues.
>
> Best regards,
> Svyatoslav R.
>
>> Artur Kowalski (4):
>>    tegra: add funcmux for exposing UART over uSD slot on Tegra 20
>>    tegra: respect CONFIG_TEGRA_ENABLE_UART* options on Transformer T20
>>    ARM: tegra: expose UART-A over uSD on Transformer T20
>>    board: asus: transformer: add DTSI file for enabling UART over uSD
>>      slot
>>
>>   .../tegra20-asus-transformer-uart-usd.dtsi    | 31 +++++++++++++++++++
>>   arch/arm/include/asm/arch-tegra20/funcmux.h   |  1 +
>>   arch/arm/mach-tegra/board.c                   |  4 ++-
>>   arch/arm/mach-tegra/tegra20/Kconfig           |  4 +++
>>   drivers/pinctrl/tegra/funcmux-tegra20.c       |  9 +++++-
>>   include/configs/transformer-t20.h             | 10 ++++++
>>   6 files changed, 57 insertions(+), 2 deletions(-)
>>   create mode 100644 arch/arm/dts/tegra20-asus-transformer-uart-usd.dtsi
>>
>> --
>> 2.48.1
>>