Mini UART on RaspberryPi CM3/CM3+

[Ahmad Fatoum]

Hi,

On 10/17/20 1:31 PM, Robert Carnecky (Neopsis) wrote:
> Finally, I managed to boot into barebox menu using UART1 (/dev/ttyS0)
> as the console. The solution was to remove all UART related overlays
> from config.txt and only activate UART1.
> 
>    enable_uart=1
> 
> Anyway, another problem occurred. When booting via barebox the CPU
> serial number is wrong. Obviously, barebox somehow manipulates the
> internal structures and
> 
>    cat /proc/cpuinfo
> 
> returns always
> 
>    Hardware        : BCM2835
>    Revision          : 0000
>    Serial              : 0000000000000000
>    Model              : Raspberry Pi Compute Module 3 IO board V3.0
> 
> When I boot the same image directly without barebox boot loader, the
> info is OK.  I found some discussions about U-Boot and wrong serial
> number here
> 
>   https://www.raspberrypi.org/forums/viewtopic.php?t=183474#p1162778
> 
> maybe that's barebox related too. Anyway, that is a definitive no go
> with barebox for us because parts of our software are expecting the
> unique serial number.

I believe you can boot Linux with /vc.dtb and you'll get the same
device tree passed to Linux as if you booted without passing through
barebox.

> 
> Robert
> 
> 
> On Fri, Oct 9, 2020 at 4:18 PM Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
>>
>> 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
>>
>> --
>> Pengutronix e.K.                           |                             |
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> 

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |