[U-Boot] [PATCH V2] add README.distro file

[Stephen Warren <swarren@wwwdotorg.org>]

On 01/10/2015 11:44 AM, Dennis Gilmore wrote:
> On Mon, 05 Jan 2015 12:55:46 -0700
> Stephen Warren <swarren@wwwdotorg.org> wrote:
>
>> On 12/28/2014 03:09 AM, Ian Campbell wrote:
>>> On Mon, 2014-12-22 at 13:46 -0700, Stephen Warren wrote:
>>>> [...]
>>>> +
>>>> +The U-Boot "syslinux" and "pxe boot" commands require a number of
>>>> environment +variables be set. Default values for these variables
>>>> are often hard-coded into +CONFIG_EXTRA_ENV_SETTINGS in the
>>>> board's U-Boot configuration file, so that +the user doesn't have
>>>> to configure them. +
>>>> +fdt_addr:
>>>> +
>>>> +  Optional. If specified a dtb to boot the system must be
>>>> available at the
>>>> +  given address.
>>>> +
>>>> +fdt_addr_r:
>>>> +
>>>> +  Mandatory.
>>>
>>> Isn't this one only mandatory if ${fdt_addr} is not given?
>>
>> Yes. I guess it's mandatory for at least one of fdt_addr or
>> fdt_addr_r to be set, according to common/cmd_pxe.c:
 >
> fdt_addr_r is actually mandatory unless you do not support device
> tree at all, which is not expected at all anymore. The reason being
> that the user/distro can override the vendor supplied dtb for whatever
> reason, by supplying a fdt/dtb fdtdir/dtbdir entry in extlinux.conf  in
> the past at times on calxeda hardware we had to override the dtb to work
> with newer kernels until we could update the systems firmware.

That's a good point. I'll revise the README again and repost a V4.