Mini UART on RaspberryPi CM3/CM3+

[Ahmad Fatoum]

Hello,

On 10/18/20 1:17 AM, Robert Carnecky (Neopsis) wrote:
> On Sat, Oct 17, 2020 at 11:29 PM Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
>>
>> 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.
> 
> Yes, but then I lose my Linux console! A summary, in all cases Barebox device
> tree in arch/arm/dts/bcm2837-rpi-cm3.dts was updated following your hint, e.g.
> 
> / {
>   chosen {
>      stdout-path = "&uart1";
>   };
>  };
> 
> &uart1 {
>         pinctrl-names = "default";
>         pinctrl-0 = <&uart1_gpio14>;
>         status = "okay";
>  };
> 
> &uart0 {
>      pinctrl-names = "default";
>      pinctrl-0 = <&uart0_gpio32>;
>      status = "okay";
>  };
> 
> 1. Booting kernel direct, works as expected (console on uart1),
> expected behavior
> 
> kernel=zImage
> enable_uart=1
> dtoverlay=uart0,txd0_pin=32,rxd0_pin=33,pin_func=7
> dtoverlay=uart1,txd1_pin=14,rxd1_pin=15
> 
> 2. With Barebox loader. The same config.txt as in case 1),
>     - no Barebox console
>     - kernel boots with the console on uart1
> 
> kernel=barebox-raspberry-pi-cm3.img
> enable_uart=1
> dtoverlay=uart0,txd0_pin=32,rxd0_pin=33,pin_func=7
> dtoverlay=uart1,txd1_pin=14,rxd1_pin=15
> 
> 3.  With Barebox loader, no uart overlays in config.txt.
>     - Barebox console on uart1 ok,
>     - kernel console on uart1
>     - almost done), but ... no cpuinfo
> 
> kernel=barebox-raspberry-pi-cm3.img
> enable_uart=1
> 
> 4. With Barebox loader, no uart overlays in config.txt, Linux boots with vc.dtb.
>     - Barebox console on uart1 ok
>     - no Linux console, Linux boots with cpuinfo ok
> 
> kernel=barebox-raspberry-pi-cm3.img
> enable_uart=1
> 
> I did not found any combination when I get the Barebox console and
> Linux console on uart1
> and with cpuinfo ok. If the serial number is not needed, case 3) should be ok.

What happens if you combine 2. and 4. ?
So you have enable_uart=1, the uart overlays _and_ Linux boots with vc.dtb?

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

-- 
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 |