[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger <wg@grandegger.com>]

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.