Re: Boot failures in -next due to 'ARM: dts: imx: Remove skeleton.dtsi'

[Guenter Roeck <linux@roeck-us.net>]

On 11/17/2016 08:39 AM, Mark Rutland wrote:
> On Thu, Nov 17, 2016 at 08:17:00AM -0800, Guenter Roeck wrote:
>> On 11/17/2016 07:05 AM, Mark Rutland wrote:
>>> On Thu, Nov 17, 2016 at 06:44:55AM -0800, Guenter Roeck wrote:
>>>> On 11/17/2016 02:55 AM, Mark Rutland wrote:
>>>>> Memory nodes require this property per ePAPR and the devicetree.org
>>>>> spec, so the bug is that we didn't add those when removing the
>>>>> skeleton.dtsi include.
>>>>
>>>> The downside from qemu perspective is that the real hardware seems
>>>> to add the property unconditionally, or the boot failure would have
>>>> been seen there as well.
>>>>
>>>> I submitted https://patchwork.ozlabs.org/patch/695951/; we'll see how it goes.
>>>
>>> Sure, the firmare/bootlaoder you're using may add this automatically.
>>>
>>> My worry is that adding this to a generic file in QEMU only serves to
>>> mask this class of bug for other boards (i.e. they'll work fine in QEMU,
>>> but not on real HW using whatever bootlaoder happens ot be there).
>>>
>> Good point.
>>
>> What would be the correct behavior for qemu ? Adding a chosen node if it does
>> not exist is one detail we already established. Also, I think a check if
>> /memory/device_type exists (and to bail out if it doesn't) would make sense.
>
> We'd also need to check for /memory@<n> nodes, as they can validly have
> unit-addresses (and many do).
>
> Generally, the "correct" way to find them is to iterate over all ndoes
> with device_type = "memory", so one could do that and give up if none
> are found, ignoring the naming entirely.
>
>> What about the memory node ? Does it have to exist, or should it be added
>> (including the device_type property) if not ?
>
> I'm not sure what QEMU does in this area. I suspect it may expect a node
> in some cases, or may generate one in others.
>
> There's no point generating one when we don't have the information to
> hand, certainly.
>
So far, for arm, qemu assumes that the /memory node exists, and it fills in
/memory/reg. This is done if a devicetree file is specified and numa is disabled.

Numa node handling is different; if NUMA is enabled, qemu removes an existing
/memory node and creates /memory@ nodes as configured. It does not expect
to see pre-existing /memory@ nodes.

Thanks,
Guenter