[PATCH v1 1/3] ARM: dts: am335x-bone: add support for beaglebone NAND cape

[Robert Nelson]

On Thu, Mar 13, 2014 at 8:03 AM, Nishanth Menon <nm at ti.com> wrote:
> On 03/13/2014 01:19 AM, Gupta, Pekon wrote:
> [..]
>>> diff --git a/arch/arm/boot/dts/am335x-bone-memory-cape.dts b/arch/arm/boot/dts/am335x-bone-memory-cape.dts
>>> new file mode 100644
>>> index 0000000..7ab088d
>>> --- /dev/null
>>> +++ b/arch/arm/boot/dts/am335x-bone-memory-cape.dts
>>>
>> From discussions, option I could think are..
>>
>> (a) NAND cape node added in both 'am335x-bone.dts' and
>>    'am335x-boneblack.dts' but "disabled" by default.
>>
>> (b) NAND cape node in new '.dts' file (as mentioned above), and generate
>>    a separate blob individual for cape.
>>
>> (c) NAND cape node in existing 'am335x-bone-common.dtsi', "disabled"
>>    by default. But there is no guarantee that future boards remain
>>    compatible and same 'common_xx.dtsi' can be reused later.
>>
>> I'll wait for Tony/Benoit-C. to decide on what suits them, as they are the
>> ones who have to maintain all these. Tony ?
>>
>
> Key for us is that we'd have to live with what ever we introduce in
> the interest of backward dtb compatibility. both (a) and (c) requires
> hand modification by user of nand cape - considering this might be the
> strategy for "most common capes", we might end up with confusing
> entries that in many cases will require additional documentation
> example: option a, c: consider both audio cape (which needs hdmi
> disabled) and nand cape (which needs mmc2 disabled) - how'd the user
> know which entries to enable/disable for the user of the cape -
> documentation needed and potentially user error prone implementation
> as well.
>
> There is as well a option (d) where we wait for FDT overlay to mature,
> write up a resource manager and support all level capes.

(b) is the direction i'm currently trying to transition the
beagleboard.org community till (d) actually shows any life/hope again.

example:
https://github.com/RobertCNelson/linux-dev/tree/am33x-v3.13/patches/static-capes

I really like Nishanth's simpler version he posted, so I'll be
converting mine to that style later today.

Also with u-boot v2014.04-rcX we now have "test -e" (exist support) so
we can actively check for the presence of <board>-<cape>.dtb and
safely fall back to <board>.dtb if it didn't actually exist.  The only
requirement is the end user specify the <cape> as a variable in
uEnv.txt

https://github.com/RobertCNelson/Bootloader-Builder/blob/master/patches/v2014.04-rc2/0001-am335x_evm-uEnv.txt-bootz-n-fixes.patch#L76

Regards,

-- 
Robert Nelson
http://www.rcn-ee.com/