Re: x86: Boot failure on select chromebooks with v6.15-rc5

From: Vignesh Raman
Date: Fri May 09 2025 - 03:38:20 EST


Hi Ingo,

On 09/05/25 12:07, Ingo Molnar wrote:

* Vignesh Raman <vignesh.raman@xxxxxxxxxxxxx> wrote:

What boot cmdline does your kernel have? The MMIO-UART patches should
only have an effect if the feature is specifically enabled via a boot
option:

+ if (!strncmp(buf, "mmio32", 6)) {
+ buf += 6;
+ early_mmio_serial_init(buf);
+ early_console_register(&early_serial_console, keep);
+ buf += 4;
+ }


amdgpu:stoney:
earlyprintk=uart8250,mmio32,0xfedc6000,115200n8 console=ttyS0,115200n8
root=/dev/nfs rw nfsroot=192.168.201.1:/var/lib/lava/dispatcher/tmp/18598802/extract-nfsrootfs-wgn1xjer,tcp,hard,v3
init=/init rootwait usbcore.quirks=0bda:8153:k ip=dhcp
tftpserverip=192.168.201.1

i915:amly:
earlyprintk=uart8250,mmio32,0xde000000,115200n8 console=ttyS0,115200n8
root=/dev/nfs rw nfsroot=192.168.201.1:/var/lib/lava/dispatcher/tmp/18598804/extract-nfsrootfs-5rlm_b6z,tcp,hard,v3
init=/init rootwait usbcore.quirks=0bda:8153:k ip=dhcp
tftpserverip=192.168.201.1

i915:whl:
earlyprintk=uart8250,mmio32,0xde000000,115200n8 console=ttyS0,115200n8
root=/dev/nfs rw nfsroot=192.168.201.1:/var/lib/lava/dispatcher/tmp/18598833/extract-nfsrootfs-3w0w5_mi,tcp,hard,v3
init=/init rootwait usbcore.quirks=0bda:8153:k ip=dhcp
tftpserverip=192.168.201.1

Well, if you remove the earlyprintk option then it will boot fine,
right?

Yes, it works when mmio32 option is removed.

https://gitlab.freedesktop.org/vigneshraman/linux/-/jobs/76005338

earlyprintk=uart8250,0xde000000,115200n8 console=ttyS0,115200n8 root=/dev/nfs rw nfsroot=192.168.201.1:/var/lib/lava/dispatcher/tmp/18599938/extract-nfsrootfs-neuejjq0,tcp,hard,v3 init=/init rootwait usbcore.quirks=0bda:8153:k ip=dhcp tftpserverip=192.168.201.1


The earlyprintk=mmio32 in v6.15 is a new debugging feature that was
tested on a single board by Denis Mukhin AFAIK, and it may or may not
work on your particular UART - even assuming that all the parameters
are correct.

So the earlyprintk=mmio32 debugging feature is needed only for v6.15 and is not necessary in previous kernels (e.g., v6.14 and earlier). Is my understanding correct?

Regards,
Vignesh


Thanks,

Ingo