[Bug 194121] New: device.hints not honored when selecting UART for system console

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=194121

            Bug ID: 194121
           Summary: device.hints not honored when selecting UART for
                    system console
           Product: Base System
           Version: 10.0-STABLE
          Hardware: amd64
                OS: Any
            Status: Needs Triage
          Severity: Affects Some People
          Priority: ---
         Component: misc
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: mgsmith at netgate.com

I am trying to boot 10-STABLE on a system based on Intel's Atom C2538 board
with 2 UART devices. The first UART is not used. The second is exposed
externally to be used as the system console. When I try to set
hint.uart.1.flags="0x10" and unset that flag from UART 0, nothing gets
displayed to the system console when it boots.

I repeated the test on a SuperMicro system based on Intel's Atom C2758 board
and got similar results. Trying to force the second serial port to be the
system console doesn't work. If I set the flag to indicate that the second uart
is available as the system console, when the system comes up, the first uart is
still acting as the console. Here are the hints:

hint.uart.0.at="isa"
hint.uart.0.port="0x3F8"
hint.uart.0.irq="4"
hint.uart.1.at="isa"
hint.uart.1.port="0x2F8"
hint.uart.1.irq="3"
hint.uart.1.flags="0x10"

and the relevant info from dmesg:

uart0: <16550 or compatible> port 0x3f8-0x3ff irq 4 on acpi0
uart0: console (115200,n,8,1)
uart1: <16550 or compatible> port 0x2f8-0x2ff irq 3 flags 0x10 on acpi0

I've tried other tricks:

1. Comment out the hints listed above and just add a new set of hints for
uart.0 that has irq 3, port 0x2f8, flags 0x10. The result was that the system
still found the other uart and made it the system console. dmesg data:

uart1: <16550 or compatible> port 0x3f8-0x3ff irq 4 on acpi0
uart1: console (115200,n,8,1)
uart0: <16550 or compatible> port 0x2f8-0x2ff irq 3 flags 0x10 on acpi0

2. Set hint.uart.0.disabled="1" with the hints listed above. The result was
that the system did not output any console messages on either serial port and
just used the VGA.

In all of this testing, I had both ttyu0 and ttyu1 enabled in /etc/ttys.
/boot/loader.conf had console="comconsole,vidconsole" and
comconsole_speed="115200". /boot.config contained -D.

I can boot both of these devices from FreeBSD 8.3 with the second serial port
set as the system console. Newer versions of FreeBSD, at least 10-STABLE and
11-CURRENT, it doesn't seem to work. I haven't tried any of the 9.x releases.

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