linux-kernel - Re: [PATCH] ARM: /proc/cpuinfo: Use DT machine name when possible

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Date:	Mon, 24 Nov 2014 23:25:45 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Russell King <linux@....linux.org.uk>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Sebastian Reichel <sre@...ian.org>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Pavel Machek <pavel@....cz>,
	Fabio Estevam <festevam@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: /proc/cpuinfo: Use DT machine name when possible

On Friday 05 September 2014 15:58:16 Mark Rutland wrote:
> On Fri, Sep 05, 2014 at 02:52:05PM +0100, Pali Rohár wrote:
> > On Friday 05 September 2014 15:45:42 Mark Rutland wrote:
> > > On Fri, Sep 05, 2014 at 12:38:40PM +0100, Pali Rohár wrote:
> > > > On Wednesday 18 June 2014 18:54:24 Pali Rohár wrote:
> > > > > Machine name from board description is some generic
> > > > > name on DT kernel. DT provides machine name property
> > > > > which is specific for board, so use it instead
> > > > > generic one when possible.
> > > > > 
> > > > > Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> > > > > ---
> > > > > 
> > > > >  arch/arm/kernel/setup.c |    7 +++++--
> > > > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/arch/arm/kernel/setup.c
> > > > > b/arch/arm/kernel/setup.c index 8a16ee5..fbc7b4f
> > > > > 100644 --- a/arch/arm/kernel/setup.c
> > > > > +++ b/arch/arm/kernel/setup.c
> > > > > @@ -875,10 +875,13 @@ void __init setup_arch(char
> > > > > **cmdline_p)
> > > > > 
> > > > >  	setup_processor();
> > > > >  	mdesc = setup_machine_fdt(__atags_pointer);
> > > > > 
> > > > > -	if (!mdesc)
> > > > > +	if (mdesc)
> > > > > +		machine_name = of_flat_dt_get_machine_name();
> > > > > +	else
> > > > > 
> > > > >  		mdesc = setup_machine_tags(__atags_pointer,
> > > > > 
> > > > > __machine_arch_type); machine_desc = mdesc;
> > > > > -	machine_name = mdesc->name;
> > > > > +	if (!machine_name)
> > > > > +		machine_name = mdesc->name;
> > > > > 
> > > > >  	if (mdesc->reboot_mode != REBOOT_HARD)
> > > > >  	
> > > > >  		reboot_mode = mdesc->reboot_mode;
> > > > 
> > > > So, do you really want to break userspace which reading
> > > > file /proc/cpuinfo (after migration from boardcode -->
> > > > DT)?
> > > 
> > > You have no guarantee model name in the DT == the name in
> > > a board file anyhow, and trying to force that is wrong.
> > > So further to Russell's reply, I must NAK this from a DT
> > > perspective.
> > > 
> > > Realistically your userspace is already broken if relying
> > > on such things. You built something that only ever worked
> > > for a particular arbitrary string. So it was already
> > > broken for every other board, and there was never any
> > > guarantee that new boards where your userspace could have
> > > worked would share the same name.
> > > 
> > > You're trying to fix the wrong side of the equation.
> > > 
> > > Mark.
> > 
> > So what is your suggestion for identifing board (name/type)
> > which will work with any kernel (and will not be broken
> > again by kernel later)?
> 
> Without knowing your use case I have no idea if that's even a
> sane thing to do.
> 
> Mark.

Read information which was previously (non DT boot) in file: 
/proc/cpuinfo

Hardware        : Nokia RX-51 board
Revision        : 0012
Serial          : 0000000000000000

Userspace applications using them for identifying on which device 
and hw revisions are running.

-- 
Pali Rohár
pali.rohar@...il.com

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