Re: Mini UART on RaspberryPi CM3/CM3+

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

On Tue, Oct 20, 2020 at 6:04 AM Rouven Czerwinski
<r.czerwinski@pengutronix.de> wrote:
>
> On Tue, 2020-10-20 at 05:59 +0200, Rouven Czerwinski wrote:
> > On Tue, 2020-10-20 at 00:29 +0200, Robert Carnecky (Neopsis) wrote:
> > > 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.
> >
> > Hi,
> >
> > looking into arch/arm/dts/bcm2837-rpi-cm3.dts:
> > / {
> >         chosen {
> >                 stdout-path = &uart0;
> >         };
> > };
> >
> > The CM3 module is currently default configured to use uart0 as the
> > stdout path, while bcm2837-rpi-3.dts is configured for uart1.
> > This was done in ab76f9d09d3b7b77fc00d84bc2fac6bfbf82c69c after the
> > miniuart support was added to the NS16550 driver
> > in 77de547cd179b910cdcb8530df15d77a0fc66a3c.
>
> Disregard this, I didn't read the whole thread. There however was
> another user who tried to use the miniuart and had failures on probe on
> the CM3. Unfortunately the barebox archives don't have these mails,
> I'll attach an mbox which has the whole thread.
>
>
> Regards,
> Rouven Czerwinski
>

The thread sent by Rouven describes really the same issue and, like
me, without a solution.
As I wrote in my summary, there is one combination of config.txt and barebox
device tree booting into barebox console on uart1 and kernel console on uart1:

barebox device tree:

/ {
  chosen {
     stdout-path = "&uart1";
  };
 };

&uart1 {
        pinctrl-names = "default";
        pinctrl-0 = <&uart1_gpio14>;
        status = "okay";
 };

&uart0 {
     pinctrl-names = "default";
     pinctrl-0 = <&uart0_gpio32>;
     status = "okay";
 };


config.txt:
kernel=barebox-raspberry-pi-cm3.img
enable_uart=1

Unfortunately, in this case the content of /proc/cpuinfo in Linux is  wrong,
which is in my opinion barebox bug.

Robert

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