[U-Boot] [PATCH] powerpc: add support for the Freescale P1022DS reference board

[Scott Wood]

On 05/27/2010 02:53 PM, Wolfgang Denk wrote:
> Dear Scott Wood,
>
> In message<20100527190340.GA5915 at schlenkerla.am.freescale.net>  you wrote:
>>
>> Passing the actual, known size of RAM (why guess when we know?) as "maxsize"
>> should eliminate the machine check problem[1] -- you'd just be using it as a
>> not particularly exhaustive memory tester.  I don't see why it should be
>> mandatory.
>
> Typically we chose  "maxsize" to b twice the actual possible maximum
> to allow for real testing.

If you set maxsize beyond what you expect to find, how are you going to 
constrain it to operating on one bank?

>> It also doesn't handle non-power-of-two sized memory -- don't rely on the
>> value it returns.
>
> Such configurations are usually set up of from several differently
> sized banks of memory, and get_ram_size() is always run per bank. So
> as long as chip manufacturers continue to make RAM chips with
> power-of-two sizes only, everything should be fine.

So it's not the board code at all that should be calling this, it's the 
SDRAM code?  Which is already in u-boot, and not in this patch (other 
than some board-specific tweaks)?

>> [1] It's worse than machine checks, what if some I/O device is mapped
>> directly after RAM?  IIRC people have run into this sort of problem doing
>> this type of memory sizing on PCs.
>
> Well, let's call this a bug in setting up the memory map for the
> system ;-)

Let's not.  It can be crowded enough as is, we don't need more 
restrictions coming from u-boot wanting to do questionable and 
unnecessary things.

-Scott