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

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Message-ID: <6c187b50-8ac0-42ac-af46-5357a26cb830@collabora.com>
Date: Wed, 14 May 2025 15:27:55 +0530
From: Vignesh Raman <vignesh.raman@...labora.com>
To: dmkhn@...ton.me
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 Denis

On 12/05/25 23:00, dmkhn@...ton.me wrote:
> 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
> 
> ?

This option didn’t work. For now, we’ll use earlycon instead of 
earlyprintk to fix the issue.

Thanks.

Regards,
Vignesh

> 
> 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
>