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

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Date:	Mon, 24 Nov 2014 23:29:54 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Andreas Färber <afaerber@...e.de>
Cc:	Mark Rutland <mark.rutland@....com>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Russell King <linux@....linux.org.uk>,
	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 Saturday 06 September 2014 17:34:47 Andreas Färber wrote:
> Am 05.09.2014 15:52, schrieb Pali Rohár:
> > 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.
> > 
> > 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)?
> 
> /proc/device-tree/compatible should give you a nul-separated
> list of compatible strings for the machine. Ideally they're
> even documented under Documentation/devicetree/bindings/arm/.
> 
> But as Mark said, depending on what you are actually trying to
> distinguish in userspace, there may be better ways.
> 
> Regards,
> Andreas

Ok, this is better. It at least output that device is Nokia N900 
and not some generic omap device...

$ cat /proc/device-tree/compatible
nokia,omap3-n900ti,omap3430ti,omap3

But I need also serial number and hw revisions which are reported 
by bootloader in ATAGs.

-- 
Pali Rohár
pali.rohar@...il.com

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