[U-Boot] [PATCH] arm: pxa: PXA270 D-Cache as ram

[Sergey Yanovich]

Dear Marek Vasut,

On Tue, 2013-05-21 at 12:54 +0200, Marek Vasut wrote:
> SRAM is just the in-CPU bit of fast RAM. What do you mean by "battery-backup" ?

Yes, you are right. It is 'for high speed code or data storage preserved
during low-power states' using a quote from PXA270 EMTS (top of page 1).
Battery-backup is optional. I mixed PXA270 and LP-8x4x specs.

> > It can be used as a ultra-fast persistent
> > storage in OS. Wasting a quater of it just to boot the system isn't the
> > best choice.
> 
> The SRAM is used for stack in U-Boot until you leave board_init_f, then the 
> stack is relocated to DRAM. The OS can use SRAM as needed, U-Boot is no longer 
> operational once you load subsequent OS. What's the problem?

Anyway, SRAM preserves its state when power is off. Poweroff time could
be in years with a backup battery. In addition, D-Cache is an order of
magnitude faster than SRAM (approx. 9 times) for both reads and writes.