[Arm-netbook] motherboard negotiation

[jonsmirl at gmail.com]

On Fri, Jan 13, 2012 at 2:48 PM, lkcl luke <luke.leighton at gmail.com> wrote:
> On Fri, Jan 13, 2012 at 5:43 PM, jonsmirl at gmail.com <jonsmirl at gmail.com> wrote:
>> On Fri, Jan 13, 2012 at 11:09 AM, lkcl luke <luke.leighton at gmail.com> wrote:
>>> ok, separate discussion
>>>
>>> i'd taken into consideration being able to identify motherboards, by
>>> putting in an I2C EEPROM.  various ideas included having a USB-like
>>> "category / class" thing, and also the idea of putting the linux
>>> kernel device tree data directly into the I2C EEPROM had occurred to
>>> me.
>>
>> A scheme based on device tree is probably the best bet. uboot already
>> takes the built-in device tree and adjusts it for the amount RAM,
>> flash, CPU clk speed.
>
>  ok cool, that's a good starting point
>
>> The base board will need to have some device tree nodes described in
>> the EEPROM. The uboot on the EOMA card will read these and then look
>> for markers in it's tree on where to insert these nodes. This is
>> similar to how clock speed is fixed up.
>>
>> You need to use substitution markers since EOMA board 1 might have
>> i2c-1 connected to the PCMCIA connector and board 2 might have i2c-3
>> brought out to the connector. Or it might not have anything connected.
>
>  ok, so, strictly speaking, there would need to be devicetree
> fragments, including:
>
>  * one for the LCD interface

this one is need

>  * one for the USB bus

don't need this one, USB is discoverable
node on the EOMA device tree to say that you have a USB bus

>  * one for the I2C bus

the node for the i2c bus will be in the EOMA device tree
you need nodes in the base board for the objects that are on the bus.

>  * one for SATA (or is this generic enough to just have a bit "yes or
> no" hmm no it isn't, you could have an SATA bus IC splitting to 16
> devices)

EOMA device tree has node indicating presence of SATA controller
SATA is discoverable so no need for baseboard support

>  * another for Ethernet (or is this generic enough to have one bit
> "yes or no" i think it might be)

Node for the Ethernet controller be in the EOMA tree
Node for the PHY chip, on the baseboard? where is it?

>  * 16 for each of the GPIO pins

That one is a lot more complicated if the GPIOs can be remapped into
other devices.

> i don't think it's worthwhile worrying about the expansion header.
>
> you know... this sounds like the allwinner system would actually be
> more flexible.
>
>
>> You can't put the full device tree into the baseboard since you are
>> planning on changing CPUs in the future.
>
>  ouch.  that hadn't occurred to me.
>
>  l.
>
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-- 
Jon Smirl
jonsmirl at gmail.com