[U-Boot] [PATCH v2 04/11] fdt: Add device tree memory bindings

[Simon Glass]

Hi Tom,

On 27 October 2014 08:24, Tom Rini <trini at ti.com> wrote:
> On Fri, Oct 24, 2014 at 02:04:00PM -0600, Simon Glass wrote:
>> Hi Tom,
>>
>> On 24 October 2014 12:49, Tom Rini <trini at ti.com> wrote:
>> > On Thu, Oct 23, 2014 at 06:58:50PM -0600, Simon Glass wrote:
>> >
>> >> From: Michael Pratt <mpratt at chromium.org>
>> >>
>> >> Support a default memory bank, specified in reg, as well as
>> >> board-specific memory banks in subtree board-id nodes.
>> >>
>> >> This allows memory information to be provided in the device tree,
>> >> rather than hard-coded in, which will make it simpler to handle
>> >> similar devices with different memory banks, as the board-id values
>> >> or masks can be used to match devices.
>> > [snip]
>> >> +++ b/doc/device-tree-bindings/memory/memory.txt
>> >> @@ -0,0 +1,67 @@
>> >> +* Memory binding
>> >> +
>> >> +The memory binding for U-Boot is as in the ePAPR with the following additions:
>> >
>> > I am wary of being different from ePAPR / Linux Kernel.  What do we need
>> > this for / when do we use it?
>>
>> This extends the existing binding. It allows the location and size of
>> memory to be set by a board ID. Unfortunately on sopme hardware you
>> get a hang if you try to access memory that doesn't exist, so this
>> allows the range of available memory to be defined - or at least the
>> maximum bound since we still probe the memory size within that range.
>>
>> This feature is used on several Exynos Chromebooks.
>
> So that you can use the same DT on several disjoint boards?  How does
> this work with the kernel, does U-Boot then pass along only the correct
> map?  Patches to the kernel to also deal with this?

Typically a board may have variants with different amounts of memory,
detected at run-time by GPIOs. We want the option of using the same DT
for these, similar to what the Compulab people were talking about -
otherwise we have something of an explosion of combinations.

Yes U-Boot (already) puts the correct memory map together for the
kernel, so it all works from start to finish.

Regards,
Simon