Messages in this thread Patch in this message | | | Date | Thu, 2 Jun 2022 23:09:15 +0200 | Subject | Re: Non-working serial console | From | Paul Menzel <> |
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Dear Linux folks,
Am 02.06.22 um 18:50 schrieb Paul Menzel:
> Since a while I noticed, output to the serial console with > `console=ttyS0,115200n8` does not work with the attached configuration > `defconfig-non-working-serial.txt` created by `make savedefconfig`. > Only, when with `earlyprintk=ttyS0,115200,keep` the serial console > starts working. I am able to reproduce it in QEMU. It’s reproducible > with Linus’ latest master branch. > > $ git log --oneline --no-decorate -1 > 8ab2afa23bd19 Merge tag 'for-5.19/fbdev-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev > $ qemu-system-x86_64 --version > QEMU emulator version 5.1.0 > Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers > $ qemu-system-x86_64 -kernel arch/x86/boot/bzImage -append "console=ttyS0,115200n8" -serial file:/dev/shm/kernel.txt -curses > > With `earlyprintk=` it works: > > $ qemu-system-x86_64 -kernel arch/x86/boot/bzImage -append "earlyprintk=serial console=ttyS0,115200n8" -serial file:/dev/shm/kernel.txt -curses > > Strangely, I found a different configuration, where it works, but I > didn’t see what configuration option makes the difference. > > Can you reproduce the problem with `defconfig-no-working-serial.txt`?
It turns out, the non-working configuration build the serial 8250 driver as a module (`CONFIG_SERIAL_8250=m`) instead of building it into the Linux kernel. Building it into the Linux kernel and using `CONFIG_SERIAL_8250_CONSOLE=y` fixes my issue.
``` $ diff -u .config.old .config --- .config.old 2022-05-31 18:40:31.329017225 +0200 +++ .config 2022-06-02 22:53:06.317175267 +0200 @@ -1814,6 +1814,7 @@
CONFIG_UEFI_CPER=y CONFIG_UEFI_CPER_X86=y +CONFIG_EFI_EARLYCON=y CONFIG_EFI_CUSTOM_SSDT_OVERLAYS=y # CONFIG_EFI_DISABLE_RUNTIME is not set # CONFIG_EFI_COCO_SECRET is not set @@ -2554,11 +2555,13 @@ # # Serial drivers # -CONFIG_SERIAL_8250=m +CONFIG_SERIAL_EARLYCON=y +CONFIG_SERIAL_8250=y # CONFIG_SERIAL_8250_DEPRECATED_OPTIONS is not set CONFIG_SERIAL_8250_PNP=y # CONFIG_SERIAL_8250_16550A_VARIANTS is not set # CONFIG_SERIAL_8250_FINTEK is not set +CONFIG_SERIAL_8250_CONSOLE=y CONFIG_SERIAL_8250_DMA=y # CONFIG_SERIAL_8250_PCI is not set CONFIG_SERIAL_8250_NR_UARTS=32 @@ -2575,7 +2578,8 @@ # # CONFIG_SERIAL_KGDB_NMI is not set # CONFIG_SERIAL_UARTLITE is not set -CONFIG_SERIAL_CORE=m +CONFIG_SERIAL_CORE=y +CONFIG_SERIAL_CORE_CONSOLE=y CONFIG_CONSOLE_POLL=y # CONFIG_SERIAL_JSM is not set # CONFIG_SERIAL_LANTIQ is not set @@ -2590,7 +2594,7 @@ # CONFIG_SERIAL_SPRD is not set # end of Serial drivers
-CONFIG_SERIAL_MCTRL_GPIO=m +CONFIG_SERIAL_MCTRL_GPIO=y # CONFIG_SERIAL_NONSTANDARD is not set # CONFIG_N_GSM is not set # CONFIG_NOZOMI is not set ``` The question is, if `earlyprintk=ttyS0,115200(,keep)` worked before with `CONFIG_SERIAL_8250=m`, why the driver is needed, and `console=ttyS0,…` cannot fall back to the earlyprintk driver.
Kind regards,
Paul
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