[U-Boot] [PATCH] sunxi: allow CONFIG_DEFAULT_FDT_FILE override

[Martin Kelly <mkelly@xevo.com>]

On 05/31/2018 11:15 AM, klaus.goger at theobroma-systems.com wrote:
> Hi Martin,
> 
>> On 31.05.2018, at 19:49, Martin Kelly <mkelly@xevo.com> wrote:
>>
>> On 05/23/2018 11:34 AM, Martin Kelly wrote:
>>> On 05/17/2018 05:01 AM, Maxime Ripard wrote:
>>>> On Tue, May 01, 2018 at 05:46:41PM -0700, Martin Kelly wrote:
>>>>> Currently, sunxi-common.h ignores CONFIG_DEFAULT_FDT_FILE and assumes
>>>>> the kernel fdtfile and the u-boot devicetree names are the same.
>>>>> Although this is typically the case, sometimes you might want to
>>>>> customize one of these differently, so it's useful to allow them to be
>>>>> different.
>>>>>
>>>>> Add logic in sunxi-common.h to respect CONFIG_DEFAULT_FDT_FILE, if set,
>>>>> and default to the values it currently uses.
>>>>>
>>>>> Signed-off-by: Martin Kelly <mkelly@xevo.com>
>>>>
>>>> Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
>>>>
>>>> Maxime
>>>>
>>> (ping)
>>
>> (ping again)
>>
>> Can we get this patch merged?
> 
> The else branch will never be selected.
> CONFIG_DEFAULT_FDT_FILE will be set to “” if not set by your defconfig.
> 

Thanks for noticing this; unfortunately you are right. I thought I 
tested this, but it was in the context of a larger build and I missed it.

It looks like we have two options:

(a) Test for empty string in preprocessor language. This is quite ugly 
and has some gotchas but should be doable (e.g. 
https://stackoverflow.com/questions/3781520/how-to-test-if-preprocessor-symbol-is-defined-but-has-no-value).

(b) Always use the value of CONFIG_DEFAULT_FDT_FILE and stop using 
CONFIG_DEFAULT_DEVICE_TREE as a default. In each board file, explicitly 
set CONFIG_DEFAULT_FDT_FILE to its current default. This is what other 
boards are doing.

I favor (b). If others are in favor, I'll submit a patch for it.