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

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Date:	Sat, 06 Sep 2014 17:34:47 +0200
From:	Andreas Färber <afaerber@...e.de>
To:	Pali Rohár <pali.rohar@...il.com>
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

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

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