[U-Boot] How do ARM platform initialize DDR?

[Tom Rini]

On Tue, Sep 17, 2013 at 08:59:24AM -0700, York Sun wrote:

> Albert,
> 
> Pardon me if this is a dumb question. I have been working on powerpc
> platforms in the past. Now we (the developers I work with) are exploring
> ARM cores. I am searching how memory is initialized and found different
> solutions. Some platforms have memory ready before u-boot even starts,
> some simply write to a set of registers. I understand many platforms
> don't share the IP of DDR controller. I am wondering if there is generic
> DDR driver used by many ARM platforms, like the one we have for
> powerpc/mpc85xx SoCs.

Thinking back, as a rule of thumb, PowerPC has SPD I2C data
available, usually.  That's not the rule for ARM.  One of a few choices
happen:
1) ROM sets up DDR.
2) U-Boot/SPL sets up the DDR controller.

The problem is that the DDR controller is usually vendor-specific.
Perhaps the flip-side here is that there's not so much a generic DDR
driver for mpc85xx but simply one vendor for mpc85xx.  Taking
arch/powerpc/cpu/mpc85xx/ddr-gen3.c as what you're talking about,
arch/arm/cpu/armv7/omap-common/emif-common.c would be an ARM-world
example (the 'EMIF' is found on a large variety of TI parts, not just
"omap" ones).

> 
> Regards,
> 
> York
> 
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-- 
Tom
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