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@xxxxxxxxxxxxxxxxxxxxx>
Tested-by: Matt Porter <matt.porter@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx 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
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