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

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Message-ID: <aCIwQHABCPufAQWr@kraken>
Date: Mon, 12 May 2025 17:30:45 +0000
From: dmkhn@...ton.me
To: Vignesh Raman <vignesh.raman@...labora.com>
Cc: Ingo Molnar <mingo@...nel.org>, dmukhin@...d.com, mingo@...hat.com, andriy.shevchenko@...ux.intel.com, x86@...nel.org, daniels <daniels@...labora.com>, Daniel Stone <daniel@...ishbar.org>, robdclark <robdclark@...il.com>, lumag@...nel.org, linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: x86: Boot failure on select chromebooks with v6.15-rc5

Hi, 

On Fri, May 09, 2025 at 01:07:54PM +0530, Vignesh Raman wrote:
> Hi Ingo,
> 
> On 09/05/25 12:07, Ingo Molnar wrote:
> > 
> > * Vignesh Raman <vignesh.raman@...labora.com> 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

For the above example, can you please try something like

  earlyprintk=mmio32,0xde000000,nocfg

?

In my case, configuring exact baud rate did not work. I started to dig that,
but did not finish, because `nocfg` worked (firmware happened to configure the
UART correctly). Using `nocfg` was sufficient for the system bringup debugging.

> 
> > 
> > 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.

Correct, I have tested with one board only and with limited UART configuration
combinations.

> 
> 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
> 

Thanks,
Denis