Re: Mini UART on RaspberryPi CM3/CM3+

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

On Mon, Oct 19, 2020 at 11:28 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>
> 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@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?

Negativ. Whenever I enable overlays in the config.txt that map uart0
to pin32/33 and
uart1 to pin 14/15 (console), I do not get Barebox console. It does
not depend on the device
tree passed to the kernel. This interaction between Barebox device
tree and Raspberry config.txt
overlays is a bit strange for me.

Just an idea - does Barebox fully support this hardware? From the 2835
ARM Peripherals Guide,
chapter 2.2 miniUART :

> The implemented UART is not a 16650 compatible UART However as far as possible
> the first 8 control and status registers are laid out like a 16550 UART. Al 16550 register
> bits which are not supported can be written but will be ignored and read back as 0.
> All control bits for simple UART receive/transmit operations are available.

Barebox has support for NS16650 ( CONFIG_DRIVER_SERIAL_NS16550) but not for
Raspberry miniUART.

Anyway, I am giving up. I am sure I tested all combinations of
overlays, I have written my
own dts, nothing works as I need (console=uart1, incl. proper serial
number handling).
There is no problem to get the console on uart0/ttyAMA0, but not on uart1/ttyS0.
The Raspberry way how they are handling uarts lacks all logic and is completely
unclear.

Robert


Robert






>
> >
> > 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 |
> >
>
> --
> 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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