From 3697022ce34cb6be196d62f1dbdf677bf6cabc22 Mon Sep 17 00:00:00 2001 From: Mathew McBride Date: Thu, 16 Jan 2025 12:20:56 +1100 Subject: [PATCH] armsr: add patch (hack) to enable all "default" consoles A previous change added 'console=tty1' to the default kernel command line on armsr, in order to ensure the framebuffer console is enabled on systems capable of graphics output. Unfortunately, this change broke boards that used device tree (DT) firmware with serial consoles, as the serial console specified by the system firmware (stdout-path) was no longer setup by the kernel. A bit of probing determined that the SPCR (serial port console direction table) on ACPI systems was preventing Linux from setting up a default framebuffer console on these systems (which is why console=tty1 was added). (The affected ACPI systems are usually VMs using QEMU's 'virt' machine and EDK2 firmware. The firmware on these systems does not remove the SPCR when a screen is present) So to ensure all possible systems are setup correctly, we modify the kernel so all "default" console types (serial and screen) are setup when no console= arguments are specified on the kernel command line. Signed-off-by: Mathew McBride Fixes: c099523d66a3 ("use console=tty1 to make console more readily available") Link: https://github.com/openwrt/openwrt/pull/17012 Signed-off-by: Robert Marko --- ...printk-always-setup-default-consoles.patch | 47 +++++++++++++++++++ 1 file changed, 47 insertions(+) create mode 100644 target/linux/armsr/patches-6.6/300-printk-always-setup-default-consoles.patch diff --git a/target/linux/armsr/patches-6.6/300-printk-always-setup-default-consoles.patch b/target/linux/armsr/patches-6.6/300-printk-always-setup-default-consoles.patch new file mode 100644 index 00000000000..c7a119cff15 --- /dev/null +++ b/target/linux/armsr/patches-6.6/300-printk-always-setup-default-consoles.patch @@ -0,0 +1,47 @@ +From 0059efbd0f9c291795078fb4e50722641d525f38 Mon Sep 17 00:00:00 2001 +From: Mathew McBride +Date: Thu, 16 Jan 2025 11:48:44 +1100 +Subject: [PATCH] printk: always setup default (tty0 + stdout / SPCR) consoles + when no console= present + +(This is a hack specific to OpenWrt's armsr target) + +This change resolves a difference in behaviour between arm64 ACPI +and DT systems. +Our usecase is to ensure the system console is always present +regardless of display mode (serial port or screen). + +Both ACPI and DT have mechanisms to setup a serial console from +information passed by firmware (SPCR and stdout-path respectively). + +On ACPI systems, the SPCR table is parsed very early on in the kernel +boot which prevents the screen console (tty0) from appearing if it is +not explicitly set. + +We would like to avoid specifying console= arguments as there are many +possible configurations on the serial side (like ttyS0, ttyAMA0, ttymxc0 +etc.). + +If the kernel does not consume the serial port in SPCR/stdout-path, +then the 'default' settings from the firmware (baud rate etc.) are lost. + +If the system administrator explicitly specifies a console= argument, +then the old behaviour is returned. + +Signed-off-by: Mathew McBride +Link: https://github.com/openwrt/openwrt/pull/17012#issuecomment-2591751115 +--- + kernel/printk/printk.c | 2 +- + 1 file changed, 1 insertion(+), 1 deletion(-) + +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -3505,7 +3505,7 @@ void register_console(struct console *ne + * Note that a console with tty binding will have CON_CONSDEV + * flag set and will be first in the list. + */ +- if (preferred_console < 0) { ++ if (!console_set_on_cmdline) { + if (hlist_empty(&console_list) || !console_first()->device || + console_first()->flags & CON_BOOT) { + try_enable_default_console(newcon);