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

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Date:	Wed, 18 Jun 2014 21:22:29 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Will Deacon <will.deacon@....com>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Sebastian Reichel <sre@...ian.org>,
	Pavel Machek <pavel@....cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"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 Wednesday 18 June 2014 21:07:35 Rob Herring wrote:
> On Wed, Jun 18, 2014 at 11:54 AM, Pali Rohár 
<pali.rohar@...il.com> 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;
> 
> I did a similar patch previously[1]. Like my original patch,
> your patch unconditionally changes the name which could be
> considered part of the userspace ABI. It's arguably not good
> practice for userspace to depend on the name, but there are
> likely cases that do. So I think this needs to be optional
> and only use the DT name if the machine desc name is NULL.
> 
> So something like the below and then change the machine
> descriptors you care about. The default generic DT machine
> desc should definitely be changed.
> 
> I had a follow-up discussion with Grant about his concerns in
> the thread about knowing which machine desc used to boot. He
> said he was okay if just the machine desc address is printed
> out.
> 
> 
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 50e198c..1479250 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -887,7 +887,7 @@ void __init setup_arch(char **cmdline_p)
>         if (!mdesc)
>                 mdesc = setup_machine_tags(__atags_pointer,
> __machine_arch_type);
>         machine_desc = mdesc;
> -       machine_name = mdesc->name;
> +       machine_name = mdesc->name ? mdesc->name :
> of_flat_dt_get_machine_name();
> 
>         if (mdesc->reboot_mode != REBOOT_HARD)
>                 reboot_mode = mdesc->reboot_mode;
> 
> 
> [1]
> http://lists.infradead.org/pipermail/linux-arm-kernel/2013-No
> vember/208878.html

Hi,

now legacy board code for Nokia N900 (RX-51) is migrating to DT  
kernel and there is problem with info which /proc/cpuinfo reports

New DT kernel (3.16-rc1) reports:

# busybox cat /proc/cpuinfo 
processor       : 0
model name      : ARMv7 Processor rev 3 (v7l)
Features        : swp half thumb fastmult vfp edsp thumbee neon 
vfpv3 tls vfpd32 
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0xc08
CPU revision    : 3

Hardware        : Generic OMAP3 (Flattened Device Tree)
Revision        : 0000
Serial          : 0000000000000000

But legacy board code kernel reports:

# busybox cat /proc/cpuinfo 
processor       : 0
model name      : ARMv7 Processor rev 3 (v7l)
Features        : swp half thumb fastmult vfp edsp thumbee neon 
vfpv3 tls vfpd32 
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0xc08
CPU revision    : 3

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

Basically in DT kernel is missing Hardware, Revision and probably 
also Serial key. (Now I used only qemu for testing which set 
serial key to 0). All these informations is used by userspace 
applications which determinate how to behave.

So without this patch DT migration for Nokia N900 cannot be done 
without breaking userspace - which is not acceptable...

Also I still did not know why DT kernel does not report Revision 
number which is passed by bootloader via atags. Any idea?

-- 
Pali Rohár
pali.rohar@...il.com

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