Instead of requiring exactly one serial device and assuming ttyS0,
extract the COM port index from the ACPI device path and use the
uart I/O port address format for the console= kernel argument.
On x86, the ACPI UID for PNP0501 (16550 UART) maps directly to the
COM port number: UID 0 = COM1 (0x3F8), UID 1 = COM2 (0x2F8), etc.
The I/O port addresses are fixed in the kernel (see
arch/x86/include/asm/serial.h). Using the console=uart,io,<addr>
format (see Documentation/admin-guide/kernel-parameters.txt) addresses
the UART by I/O port directly rather than relying on ttyS naming,
and also provides early console output before the full serial driver
loads.
Restrict the entire serial console auto-detection to x86. On non-x86
(e.g. ARM with PL011 UARTs), displays may be available without GOP
(e.g. simple-framebuffer via device tree), serial device indices are
assigned dynamically during probe rather than being fixed to I/O port
addresses, and the kernel has its own console auto-detection via DT
stdout-path.
When ConOut has no device path (ConSplitter), all text output handles
are enumerated. If multiple handles have PNP0501 UART nodes with
different UIDs, bail out rather than guessing.
Add ACPI_DP device path subtype, ACPI_HID_DEVICE_PATH struct, and
EISA_PNP_ID() macro to device-path.h for parsing ACPI device path
nodes. Remove MSG_UART_DP, device_path_has_uart(), count_serial_devices()
and proto/serial-io.h (no longer needed).
Move all the console logic to console.c as well.
I very much dislike the approach in which we were mixing Linux and UEFI C code
in the same subdirectory. No code was shared between two environments. This
layout was created in e7dd673d1e, with the
justification of "being more consistent with the rest of systemd", but I don't
see how it's supposed to be so.
Originally, when the C code was just a single bootctl.c file, this wasn't so
bad. But over time the userspace code grew quite a bit. With the moves done in
previuos commits, the intermediate subdirectory is now empty except for the
efi/ subdir, and this additional subdirectory level doesn't have a good
justification. The components is called "systemd-boot", not "systemd-efi", and
we can remove one level of indentation.
Daan De Meyer
Jelle van der Waa
Zbigniew Jędrzejewski-Szmek