Messages in this thread | | | Date | Mon, 09 Sep 2013 17:02:26 +0100 | From | Jonathan Austin <> | Subject | Re: [PATCHv3] ARM: OMAP2+: am335x-bone*: add DT for BeagleBone Black |
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Hi Matt,
On 09/09/13 15:16, Matt Porter wrote: > On Mon, Sep 09, 2013 at 09:59:26AM -0400, Matt Porter wrote: >> 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@dominion.thruhere.net> >>>> >>>> Tested-by: Matt Porter <matt.porter@linaro.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@vger.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. > > Sorry to reply to myself, but I probably didn't make it 100% clear as > to why this effectively fixes the problem. Both mainline u-boot *and* > the vendor u-boot have findfdt implemented to load an > am335x-boneblack.dtb based on board detection.
This makes more sense now, thanks. Not sure that it is still a good case for CC:stable. Are people currently working around findfdt failing, etc? If so, do you think backporting the fix will stop them doing that? I don't really know what the workflow looks like...
Generally the idea of backporting DT fixes to older kernels gives me the Heebie-Jeebies - this case of being able to damage hardware is a great example of why it might be scary (though I acknowledge that this specific patch is unlikely to have a bad outcome)
Jonny > > Hopefully this makes it clear why this fixes a bug in the kernel. If > you use appended dtb to include the wrong one, well, you shouldn't > be using appended dtb. It's a *hack* and loading it separately > works fine if you use the U-Boot that ships with BBB or mainline. > > -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@lists.infradead.org >>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >>>> >>> >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-omap" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >
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