linux-kernel - Re: [PATCH 3/3] of: Handle memory@0 node on PPC32 only

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Message-ID: <20140423104528.GD30036@e106331-lin.cambridge.arm.com>
Date:	Wed, 23 Apr 2014 11:45:28 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	Leif Lindholm <leif.lindholm@...aro.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robherring2@...il.com>,
	Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 3/3] of: Handle memory@0 node on PPC32 only

On Tue, Apr 22, 2014 at 02:35:15PM +0100, Grant Likely wrote:
> On Fri, 18 Apr 2014 13:59:24 +0100, Leif Lindholm <leif.lindholm@...aro.org> wrote:
> > Hi Geert,
> > 
> > On Fri, Apr 18, 2014 at 10:04:15AM +0200, Geert Uytterhoeven wrote:
> > > On Thu, Apr 17, 2014 at 7:42 PM, Leif Lindholm <leif.lindholm@...aro.org> wrote:
> > > > In order to deal with an firmware bug on a specific ppc32 platform
> > > > (longtrail), early_init_dt_scan_memory() looks for a node called
> > > > memory@0 on all platforms. Restrict this quirk to ppc32 kernels only.
> > > 
> > > This breaks backwards compatibilty with old DTSes (at least on ARM/MIPS,
> > > where you added the missing property in patches 1 and 2 of the series)?
> > 
> > As Rob said in response to 0/3, the MIPSs would likely not be affected,
> > since they embed the DT.
> > 
> > > For the Longtrail, I don't care much anymore, as mine died in 2004.
> > > AFAIK, there have never been many users anyway.
> > 
> > There are still a few mentions of it under arch/powerpc/, so I wouldn't
> > want to be the one to kill it off...
> > 
> > How about the below v2 3/3 to address the ARM platform?
> 
> The problem with this approach is that selecting one board that needs it
> automatically makes it active for all boards. It would need to be
> something more like the following:
> 
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 399e242e1a42..55d65b2b4c74 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -887,12 +887,10 @@ int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
>  
>  	/* We are scanning "memory" nodes only */
>  	if (type == NULL) {
> -		/*
> -		 * The longtrail doesn't have a device_type on the
> -		 * /memory node, so look for the node called /memory@0.
> -		 */
>  		if (depth != 1 || strcmp(uname, "memory@0") != 0)
>  			return 0;
> +		if (!of_flat_dt_match(dt_root, memory_quirk_list))
> +			return 0;
>  	} else if (strcmp(type, "memory") != 0)
>  		return 0;
>  
> With a list of compatible properties for affected boards.

That looks sane to me.

Does anyone have a LongTrail DT to hand, and if so does the root have a
compatible string? From grepping through the kernel I could only find a
model string ("IBM,LongTrail").

Is anyone aware of strings other than that and "st-ericsson,ccu8540" to
look out for?

Cheers,
Mark.
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