[U-Boot] [PATCH] ARMV7: OMAP4: Calculate SDRAM size

[V, Aneesh]

Dear Wolfgang Denk,

> -----Original Message-----
> From: Wolfgang Denk [mailto:wd at denx.de]
> Sent: Sunday, September 26, 2010 8:07 PM
> To: Nishanth Menon
> Cc: V, Aneesh; u-boot at lists.denx.de; Steve Sakoman
> Subject: Re: [U-Boot] [PATCH] ARMV7: OMAP4: Calculate SDRAM size
> 
> Dear Nishanth Menon,
> 
> In message <4C9F3E4F.3040403 at gmail.com> you wrote:
> >
> > > I think you are referring to SDRAM initialization. Yes, it is
> assumed
> > > that SDRAM initialization(at least the DMM part of it) is done
> before
> > > the call to sdram_size(). The right location for this seems
> > > to be the initial part of sdram_init().
> >
> > thanks for the clarification.. NOR boot is usually going to have
> initial
> > part in XIP -> we'd traditionally relocate to SDRAM before the
> call to
> > sdram_size() happens.
> 
> Yes, this was the way how many ARM boards id, and this is what I'm
> trying to explain: this is WRONG.
> 
> SDRAM configuration must be done while still running from NOR, i. e.
> before relocation. Only then free reconfiguration, auto-sizing etc.
> is
> possible.

We shall rework the patch to do SDRAM size calculation as part of 
'lowlevel_init' that is called before relocation. I hope that should 
solve the problem. 

Please note that we are always running from SDRAM because none of 
the OMAP4 boards so far have any XIP device.

Regarding true run-time detection of SDRAM size and configuration: 
We do not support it today. However, LPDDR2 supports Mode Registers 
that have size info and our memory controller can read it. This 
coupled with the base AC timings specified by the LPDDR2 spec 
creates the possibility of doing a truly run-time detection and 
configuration of SDRAM that works for all boards. I was indeed
thinking of trying it out sometime. Please note that the base AC
timing values may not be optimal for all memory parts.


Best regards,
Aneesh