[U-Boot-Users] Ideas on U-Boot configuration with FDT
Wolfgang Grandegger
wg at grandegger.com
Fri May 18 17:20:48 CEST 2007
Timur Tabi wrote:
> Wolfgang Grandegger wrote:
>
>> RAM is _not_ available at that stage.
>
> Do we really need RAM to parse the device tree and configure U-Boot? I
> think not.
But you need it anyhow in RAM for booting Linux. Why not doing it early,
e.g. after relocation when memory is available.
> The device tree has a memory section:
>
> memory {
> device_type = "memory";
> reg = <00000000 10000000>; // 256MB
> };
>
> So the question is: do we want U-Boot to use this node to determine how
> much RAM there is, or do we want U-Boot to determine how much RAM there
> is and update this node?
Both makes sense, I think. How we finally use FDT it U-Boot is not yet
clear, but exhaustive usage like in the kernel seems not attractive to
me. Currently I just need it do enable some devices dynamically, like
PCMCIA, RTC and CAN and configure the LCD controller for various panels.
>> Depends, you might be right for FLASH on a 32-bit bus. On slow ROM
>> devices and slow processors, it matters.
>
> I still don't see how it's important. If the device tree is on slow
> memory, so what? You have to read it sooner or later. If your board
> can't handle this feature, then don't enable it, and configure U-Boot
> the "old fashioned way".
Don't like the "don't care" argument. If you can make your code faster,
just do it.
Wolfgang.
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