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

Wolfgang Denk wd at denx.de
Fri May 18 21:04:05 CEST 2007

In message <464DBFC8.4050708 at freescale.com> you wrote:
> 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?

Tradition is that U-Boot will determine how much RAM there is, and  I
definitely  want  to  keep it that way. Among other things, this is a
cheap and yet still pretty efficient protection against most types of
RAM errors.

> I still don't see how it's important.  If the device tree is on slow memory, so what?  You 

Timu, there is lots of code in U-Boot that you haven't seen yet...

> 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".

Having  to  read  it  later  (after  relocation  into  RAM)  may   be
*significantly*  faster. We can then use buffering, while we may have
to use repeated small reads (repeated for each element we're  looking
up)  while  running from ROM. Remember that there is more things than
just NOR flash. Data may be stored in slow serial devices like EEPROM
on I2C, or serial flash on SPI, or NAND flash, etc.

Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
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Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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