Mini UART on RaspberryPi CM3/CM3+

[Ahmad Fatoum]

Hello Robert,

On 10/9/20 2:30 PM, Robert Carnecky (Neopsis) wrote:
>> Try adding to arch/arm/dts/bcm2837-rpi-cm3.dts:
>>
>> &uart1 {
>>         pinctrl-names = "default";
>>         pinctrl-0 = <&uart1_gpio14>;
>>         status = "okay";
>> };
> 
> I extended arch/arm/dts/bcm2837-rpi-cm3.dts as advised +
> additionally I set UART0 to pins 32/33.
> 
> &uart0 {
>      pinctrl-names = "default";
>      pinctrl-0 = <&uart0_gpio32>;
>      status = "okay";
> };
> 
> I still cannot see Barebox console on boot, however, the Barebox loader
> starts in 3 seconds my kernel and I get the Linux console output on
> UART1/ttyS0.

Strange that this made the kernel boot now. Maybe somewhere an unclocked
peripheral was being accessed before?

> Now my Linux boots as expected, unfortunately without
> visible Barebox console. I tried all Barebox console setting
> (NONE/ALL/FIRST), same result, no Barebox console output on UART0
> or UART1.

Huh, you did listen at the UART0 _before_ the RS-485 transceiver?
UART0 should work, at least it apparently did when the CM3 support
was added.

>> If that doesn't help, use CONSOLE_ACTIVATE_ALL and listen
>> on UART0 before the RS-485 transceiver and paste the
>> dmesg and devinfo input you get.
> 
> # dmesg | grep tty
> [    0.000000] Kernel command line: console=ttyS0,115200
> coherent_pool=1M snd_bcm2835.enable_compat_alsa=0
>  snd_bcm2835.enable_hdmi=1 snd_bcm2835.enable_headphones=1
> 8250.nr_uarts=1 bcm2708_fb.fbwidth=656
>  bcm2708_fb.fbheight=416 bcm2708_fb.fbswap=1
> smsc95xx.macaddr=B8:27:EB:C5:7D:E3 vc_mem.mem_base=0x3ec00000
>  vc_mem.mem_size=0x40000000  root=/dev/mmcblk0p2 console=ttyS0,115200
> rootfstype=ext4 elevator=deadline rootwait
> [    1.289058] printk: console [ttyS0] disabled
> [    1.289175] 3f215040.serial: ttyS0 at MMIO 0x0 (irq = 53, base_baud
> = 50000000) is a 16550
> [    1.945483] printk: console [ttyS0] enabled
> [    2.432604] 3f201000.serial: ttyAMA0 at MMIO 0x3f201000 (irq = 81,
> base_baud = 0) is a PL011 rev2
> 
> # stty -F /dev/ttyAMA0 115200
> # cat /etc/inittab  > /dev/ttyAMA0   <- OK

I meant dmesg under barebox, if UART1 fails to output, but UART0 can be
read before the transceiver.

On 10/6/20 1:32 AM, Robert Carnecky (Neopsis) wrote:
> I played a bit more with the config.txt settings and when I activated the flag
> 
>     uart_2ndstage=1
> 
> I got the barebox console! Here a snippet from the 2stage while
> logging the UART lading.

Oh. That would indicate that there is some sort of initialization missing.
uart_2ndstage=1 initializes the UART for VideoCore use apparently and from
there on, it works.

> What I do not understand: how the loaded  /mfs/sd/bcm2710-rpi-cm3.dtb
> and the overlays
> cooperate with the Barebox device tree? Does it mean we have two sets
> of device tree
> files?

Yes. The VideoCore device tree is available in barebox as /vc.dtb,
see e390c8799d91 ("ARM: rpi: save fdt that was passed from VideoCore")


Hope this helps,
Ahmad

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