linux-kernel - Re: earlyprintk=xdbc seems broken

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Date:   Tue, 25 Jan 2022 11:54:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Chunfeng Yun <chunfeng.yun@...iatek.com>
Subject: Re: earlyprintk=xdbc seems broken

On Tue, Jan 25, 2022 at 11:47:11AM +0100, Peter Zijlstra wrote:
> On Tue, Jan 25, 2022 at 10:51:00AM +0200, Mathias Nyman wrote:
> > On 24.1.2022 18.46, Peter Zijlstra wrote:
> 
> > > FYI, I'm thinking early_xdbc_parse_parameter should've now given
> > > dpgp_num: 1 ?
> > > 
> > 
> > Yes, it should. 
> > 
> > Looks like there's a parsing issue.
> > "earlyprintk=xdbc1,keep" fails on our Tigerlake as well.
> >   
> > Without the "keep" option it works for me:
> > 
> > [    0.000000] Command line: console=ttyS0,115200n8 buildroot_hostname=tgl04 earlyprintk=xdbc1 dmi_entry_point=0x74374000
> > [    0.000000] xhci_dbc:early_xdbc_parse_parameter: dbgp_num: 1
> 
> [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.16.0+ root=UUID=a652986c-fbc6-4341-85c3-b4ad4402f130 ro debug ignore_loglevel sysrq_always_enabled usbcore.autosuspend=-1 earlyprintk=xdbc1,keep force_early_printk sched_verbose ft
> race=nop mitigations=off nokaslr
> 
> [    0.000000] xhci_dbc:early_xdbc_parse_parameter: dbgp_num: 1
> 
> [    0.399988] xhci_dbc:xdbc_start: DbC is running now, control 0x8d000003 port ID 15
> [    0.399998] xhci_dbc:xdbc_handle_port_status: connect status change event
> [    0.399999] xhci_dbc:xdbc_handle_port_status: port reset change event
> [    0.431217] printk: console [earlyxdbc0] enabled
> 
> Success!! I'll go submit proper patches for this then.

Next up, I don't suppose there's working patches for GRUB ? Because the
moment the thing gets stuck on a non-working kernel I'm screwed again :/