Linux-3.14-rc2: Order of serial node compatibles in DTS files.

[Stephen N Chivers]

Sebastian Hesselbarth <sebastian.hesselbarth at gmail.com> wrote on 
02/12/2014 09:51:43 AM:

> From: Sebastian Hesselbarth <sebastian.hesselbarth at gmail.com>
> To: Kumar Gala <galak at kernel.crashing.org>, Stephen N Chivers 
> <schivers at csc.com.au>
> Cc: linuxppc-dev at lists.ozlabs.org, Chris Proctor 
> <cproctor at csc.com.au>, devicetree <devicetree at vger.kernel.org>, Arnd
> Bergmann <arnd at arndb.de>
> Date: 02/12/2014 09:51 AM
> Subject: Re: Linux-3.14-rc2: Order of serial node compatibles in DTS 
files.
> 
> On 02/11/2014 11:33 PM, Kumar Gala wrote:
> >
> > On Feb 11, 2014, at 2:57 PM, Stephen N Chivers <schivers at csc.com.au> 
wrote:
> >
> >> I have been trial booting a 3.14-rc2 kernel for a 85xx platform
> >> (dtbImage).
> >>
> >> After mounting the root filesystem there are no messages from the 
init
> >> scripts
> >> and the serial console is not available for login.
> >>
> >> In the kernel log messages there is:
> >>
> >> of_serial f1004500.serial: Unknown serial port found, ignored.
> >>
> >> The serial nodes in boards dts file are specified as:
> >>
> >>         serial0: serial at 4500 {
> >>                         cell-index = <0>;
> >>                         device_type = "serial";
> >>                         compatible = "fsl,ns16550", "ns16550";
> >>                         reg = <0x4500 0x100>;
> >>                         clock-frequency = <0>;
> >>                         interrupts = <0x2a 0x2>;
> >>                         interrupt-parent = <&mpic>;
> >>                 };
> >>
> >> Reversing the order of the compatible:
> >>
> >>         compatible = "ns16550", "fsl,ns16550";
> >>
> >> restores the serial console.
> >>
> >> Linux-3.13 does not have this behaviour.
> >>
> >> There are 49 dts files in Linux-3.14-rc2 that have the fsl,ns16550
> >> compatible first.
> >
> > Hmm,
> >
> > Wondering if this caused the issue:
> >
> > commit 105353145eafb3ea919f5cdeb652a9d8f270228e
> > Author: Sebastian Hesselbarth <sebastian.hesselbarth at gmail.com>
> > Date:   Tue Dec 3 14:52:00 2013 +0100
> >
> >      OF: base: match each node compatible against all given matches 
first
> 
> [adding Arnd on Cc]
> 
> Could be. I checked tty/serial/of_serial.c and it does not provide a
> compatible for "fsl,ns16550". Does reverting the patch fix the issue
> observed?
> 
> I don't think the missing compatible is causing it, but of_serial
> provides a DT match for .type = "serial" just to fail later on
> with the error seen above.
> 
> The commit in question reorders of_match_device in a way that match
> table order is not relevant anymore. This can cause it to match
> .type = "serial" first here.
> 
> Rather than touching the commit, I suggest to remove the problematic
> .type = "serial" from the match table. It is of no use anyway.
Deleting the "serial" line from the match table fixes the problem.
I tested it for both orderings of compatible.
> 
> Sebastian

Thanks,
Stephen Chivers,
CSC Australia Pty. Ltd.