[Arm-netbook] defining the eoma68 eeprom usage

[luke.leighton]

On Mon, Nov 4, 2013 at 8:35 PM, Arokux X <arokux at gmail.com> wrote:
> On Mon, Nov 4, 2013 at 9:30 PM, Christopher Thomas
> <christopher at firemothindustries.com> wrote:
>>
>>
>>
>> On Mon, Nov 4, 2013 at 2:05 PM, joem <joem at martindale-electric.co.uk> wrote:
>>>
>>> : yes.  my concerns here are that the EEPROM would be overwritten by
>>> :user applications otherwise, potentially destroying the ability of CPU
>>> :Cards to identify the device.
>>>
>>> I2C eeproms dirt cheap - have two eeproms - one user data (such as
>>> calibration data
>>> for instruments, keys, etc) and one for system data.
>>>
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>>
>>
>> Given the need for device-tree info, and RID, etc etc, presumably, how large
>> of an EEPROM would we technically need?
>
> Device Tree eats this much:
>
> user$ du -h arch/arm/boot/dts/*.dtb | grep sun
> 12K    arch/arm/boot/dts/sun4i-a10-a1000.dtb
> 12K    arch/arm/boot/dts/sun4i-a10-cubieboard.dtb
> 12K    arch/arm/boot/dts/sun4i-a10-hackberry.dtb
> 12K    arch/arm/boot/dts/sun4i-a10-mini-xplus.dtb
> 8.0K    arch/arm/boot/dts/sun5i-a10s-olinuxino-micro.dtb
> 8.0K    arch/arm/boot/dts/sun5i-a13-olinuxino.dtb
> 8.0K    arch/arm/boot/dts/sun6i-a31-colombus.dtb
> 12K    arch/arm/boot/dts/sun7i-a20-cubieboard2.dtb
> 12K    arch/arm/boot/dts/sun7i-a20-cubietruck.dtb
> 12K    arch/arm/boot/dts/sun7i-a20-olinuxino-micro.dtb

 it's completely unnecessary to store the *entire* devicetree on a
per-CPU basis.  and it would cause huge problems to do so.

 instead i expect the "GPIO 0 devicetree" entry to be about... 200
bytes maximum.  i expect the "GPIO 1 devicetree" entry to be about 200
bytes.  i expect the "LCD specification devicetree" entry to be about
400 bytes.  the total number of entries - even if there were 120 I2C
devices hanging off the bus - should be well below 8K.

 each of those entries _will_ need to be merged into the devicetree
arch/arm/boot/dts/sun7i-eoma68-a28.dtb at runtime (by u-boot and by
the running linux kernel).  that can be dealt with.

l.