On 12/06/2013 09:31 AM, Ian Campbell wrote:
>>>> It's good to talk about the implications. If we want to handle
>>>> downgrading of kernels with an updated flash-kernel, I think, that
>>>> cannot be done without an additional Kernel-Version field.
>>>>
>>>> This is because v3.11 ships with:
>>>>
>>>> /usr/lib/linux-image-3.11-2-kirkwood/kirkwood-sheevaplug.dtb
>>>>
>>>> But non-DT Sheeva support is still in the kernel, so non-DT Sheeva Plug
>>>> is used with current flash-kernel and v3.11. Although v3.10 and v3.11
>>>> are not Wheezy's kernels.
>>>
>>> Is 3.11+DTB actively broken though?
>>
>> v3.11+DT works on Sheeva Plug, just tested it.
> 
> That's good. Do you know if v3.10 or earlier shipped a DT in the kernel
> package?

There is no DT for Sheeva Plug in Debian's v3.10, but 25 dtb in total.

>> I was thinking of the following scenario:
>>
>> I have installed current flash-kernel (without DT support) and kernel
>> v3.11. Then the new flash-kernel with
>> append-DT-if-present-in-the-Kernel-package feature is released together
>> with a new DT only kernel (=v3.12). I upgrade, because I want to have
>> the shiny new kernel.
>>
>> For whatever reason I want to downgrade to v3.11, then I end up with
>> v3.11 with DT, because the flash-kernel is still the new one.
> 
> Right, this is the scenario I am worried about.
> 
>> The system does not behave as I expected. I downgraded to the same
>> kernel but now the DT Sheeva Plug is booted.
> 
> Ideally v3.11+DT would work well enough that the user wouldn't care
> about the difference. even if not I think so long as v3.11+DT works well
> enough to be able to manually fix things (e.g. by downgrading f-k) then
> this would be an acceptable trade-off to support such partial upgrades.

Yes works for me.

>> Although the bootloader sets the ARCH number, an attached DT seems to be
>> preferred.
> 
> That is what I would expect, yes.
> 
>>>>> I suppose it would be nice to just check that the Wheezy kernel doesn't
>>>>> complain about or get confused by the appended DTB. Can you check that?
>>>>
>>>> I don't have physical access to that Sheeva Plug.
>>>
>>> Hrm, this would be something which would be good to try somewhere.
>>
>> On Wheezy there is no Sheevaplug DTB to attach...
> 
> Oh yes, of course.
> 
>>> Now I think of it the Wheezy kirkwood kernel did have DT and
>>> APPENDED_DTB support enabled, in order to support dreamplugs.
>>
>> http://packages.debian.org/wheezy/armel/linux-image-3.2.0-4-kirkwood/filelist
>>
>> Wheezy has two dtb files:
>>
>> /usr/lib/linux-image-3.2.0-4-kirkwood/kirkwood-dreamplug.dtb
>> /usr/lib/linux-image-3.2.0-4-kirkwood/kirkwood-iconnect.dtb
>>
>>> I have a feeling that would mean that it wouldn't boot if you appended a
>>> dtb to it. Which would mean we do have to think about versioned checks
>>> or something.
>>
>> Just stating the obvious: The Sheeva Plug probably wouldn't boot if I
>> attach a dreamplug dtb to it. :)
> 
> Right, I was thinking/worrying that it won't boot if you attach any DTB
> to it, including a newer one for the shivaplug. But of course f-k
> wouldn't ever do that.
> 
> So the only concern is intermediate kernel versions which have a DT file
> but prefer non-DT operation. As I say I think so long as it boots well
> enough to allow repair then this is ok.

In Debian, v3.11 is the first kernel that ships with a Sheeva Plug DT
and that works for me.

> Do shivaplugs typically provide u-boot console access as standard or
> does that require soldering and/or cracking the case open?

No, just plug in a Mini USB Cable and you have a serial console (and a
JTAG for debricking via openocd).

Marc

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