Date:	Mon, 9 Sep 2013 09:59:26 -0400
From:	Matt Porter <matt.porter@...aro.org>
To:	Jonathan Austin <jonathan.austin@....com>
Cc:	Koen Kooi <koen@...inion.thruhere.net>,
	Mark Rutland <Mark.Rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	Pawel Moll <Pawel.Moll@....com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"tony@...mide.com" <tony@...mide.com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"bcousson@...libre.com" <bcousson@...libre.com>,
	"olof@...om.net" <olof@...om.net>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv3] ARM: OMAP2+: am335x-bone*: add DT for BeagleBone Black

On Mon, Sep 09, 2013 at 02:51:13PM +0100, Jonathan Austin wrote:
> Hi Matt,
> 
> On 09/09/13 14:31, Matt Porter wrote:
> >On Sun, Sep 08, 2013 at 01:12:26PM +0200, Koen Kooi wrote:
> >>The BeagleBone Black is basically a regular BeagleBone with eMMC and HDMI added,
> >>so create a common dtsi both can use.
> >>
> >>IMPORTANT: booting the existing am335x-bone.dts will blow up the HDMI transceiver
> >>after a dozen boots with an uSD card inserted because LDO will be at 3.3V instead
> >>of 1.8.
> >>
> >>MMC support for AM335x still isn't in, so only the LDO change has been added.
> >>
> >>Signed-off-by: Koen Kooi <koen@...inion.thruhere.net>
> >
> >Tested-by: Matt Porter <matt.porter@...aro.org>
> >
> >Works fine for me on tip and 3.11. I did notice a regression in musb (worked
> >on 3.11, now failing to probe but this is not related to your new dts as it
> >happens on am335x-bone.dts too, assuming merge window volatility). One nit,
> >git-am picked up a whitespace error on that extra line at EOF so you should
> >trim that out.
> >
> >Only thing is...for a clear bug like this that will destroy hardware, it
> >should be marked Cc: stable@...r.kernel.org to be picked up in stable.
> >
> 
> If I've understood Koen correctly then what he's saying is that if
> you *were* to use the current (before this patch) am335x-bone.dts on
> a Beagle Bone Black (which would be wrong, as that's not the board
> you have...) then things would break.
> 
> I don't see that this patch fixes that - as far as I can see, even
> after the patch, using am335x-bone.dts with a Bone Black will risk
> the damage?
> 
> If so, I don't think this is a 'stable fix' kind of thing, as it
> doesn't actually fix the problem?

It fixes the problem by providing the correct dts for BBB which the
vendor tree has had for sometime. In the absence of a specific dts
for BBB, it appears everybody (TI and OMAP maintainers, included)
has assumed that am335x-bone.dts is correct and safe.

I'm sure there's plenty of systems represented in dts/* where you
could cause damage by loading another dtb for a similar board from
the same SoC family...it's a common risk if you get the wrong dtb
with more-or-less arbitrary regulator settings.

-Matt

> 
> Koen - is there a way for a booting kernel to detect which board it
> is on and avoid any potential damage if someone gives it the wrong
> DT?
> 
> Jonny
> 
> >-Matt
> >
> >_______________________________________________
> >linux-arm-kernel mailing list
> >linux-arm-kernel@...ts.infradead.org
> >http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >
> 
> 
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