[U-Boot] [RFC] am33xx: add 600us wait in DDR3 initialization sequence

[Tom Rini]

On Wed, Jul 29, 2015 at 11:57:26AM +0000, Egli, Samuel wrote:
> Hi James,
> thank you for your reply!
> 
> > -----Original Message-----
> > From: Doublesin, James [mailto:doublesin at ti.com]
> > Sent: Dienstag, 28. Juli 2015 21:59
> > To: Egli, Samuel; 'trini at konsulko.com'; Balbi, Felipe
> > Cc: 'u-boot at lists.denx.de'; 'hs at denx.de'; 'Stefan Roese'; Meier, Roger;
> > Senn, Joerg; Belogolov, Oleg
> > Subject: RE: [RFC] am33xx: add 600us wait in DDR3 initialization sequence
> > 
> > Hi Samuel, I don't think these changes are necessary.
> > 
> > I think your concern about the initialization steps is not correct.  The
> > first setting of the REF_CTRL (before SDRAM_CONFIG write) will be used by
> > the EMIF controller to determine the delay between the rising edge of
> > DDR_RESETn and DDR_CKE.  We typically write a value of 0x3100 in REF_CTRL
> > to achieve this, which comes from this formula:
> > 
> >   (16*SDRAM_REF_CTRL)/400MHz > 500us
> 
> That's interesting. This isn't really documented in the TRM. But I see
> ddr.c:
> ...
> if (regs->zq_config)
> 		writel(0x80003100, &emif_reg[nr]->emif_sdram_ref_ctrl);
> ...
> Why does this depend on zq_config? While debugging I saw that we 

This part I can answer.  We use the same functions on DDR2 and DDR3 and
use the presence of zq_config in regs to know if this is a DDR2 or DDR3
setup.

-- 
Tom
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