Re: Mini UART on RaspberryPi CM3/CM3+

["Robert Carnecky (Neopsis)" <robert@neopsis.com>]

On Sat, Oct 17, 2020 at 11:29 PM Ahmad Fatoum <a.fatoum@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.

Robert

>
> >
> > Robert
> >
> >
> > On Fri, Oct 9, 2020 at 4:18 PM Ahmad Fatoum <a.fatoum@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 |

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