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

[Artur Kowalski]

W dniu 25.03.2025 o 08:14, Svyatoslav Ryhel pisze:

> пн, 24 бер. 2025 р. о 22:01 Artur Kowalski<arturkow2000 at gmail.com> пише:
>> 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
> It is a handy trick indeed, but it is still just a trick and not smth
> that fits mainline. Maximum I can propose is picking funcmux change
> along with uart over sd section in transformer t20 documentation.
>
>> 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.
> I am not sure what are you doing but TF101 has full support of U-Boot
> as primary bootloader along with full mainline support till 6.14
> including. It uses extlinux boot method and needs no intermediates or
> chainloading.
>
> If you wish to use U-Boot for tethered booting that is perfectly fine as well.
Booting with UEFI didn't work, I have solved that problem locally by 
forcing LMB allocator
to not allocate at 0x0, any platform where RAM starts at 0x0 could be 
affected by it. Soon I
will send patches. I want to use UEFI so that I can take advantage 
systemd-boot features such
as one-time boot for system updates, some other software I plan to use 
also depends on UEFI.
Also, with extlinux I can't use verified boot, but, eventually I plan to 
program PKC and have full
secure boot with hardware RoT.

When bringing UEFI support I also made some changes so that U-Boot works 
with
CONFIG_OF_UPSTREAM, I also plan to upstream the patches soon.

Linux lacks GPS support and possibly camera, also sorry for my mistake, 
I meant a complete Linux
distro rather than the kernel only, which is lacking GPU acceleration. 
Also, when running preemptible
kernel I can see multiple "scheduling while atomic" errors and random 
system freezes under load.
>> 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.
>>
> I am fine with any changes which may simplify debugging for you as
> long as they do not invade into completed device configuration without
> a valid reason. Device must expose a dedicated UART for debug, not a
> mux which breaks some device features just because you do not want to
> contain them locally.
>
> For example, patches which add UART-E support along with funcmux
> change which exposes uart-e over usd were accepted, but patch similar
> to yours which would reconfigure usd to uart for surface rt or p880
> would be rejected.

I've sent v2, which besides few other fixes, adds dedicated Kconfig 
option for enabling UART. If disabled, the config is the same.

>> 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.

Turns out it was something else. I've sent a patch to fix that:

https://patchwork.ozlabs.org/project/uboot/patch/20250330211153.RFC.1.Iebf436d41ff5f52c0b11aaf9e8f98d6a2d4d56bc@changeid/

>> 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
>>>>