[U-Boot] [PATCH] i.MX28: Add delay after CPU bypass is cleared

[Marek Vasut <marex@denx.de>]

Dear Stefano Babic,

> On 04/05/2012 13:32, Marek Vasut wrote:
> > This solves issues when larger amount of DRAM is used, like 256MB.
> > Behave the same in case of CPU bypass as we do in case of EMI
> > bypass, but wait 15 ms. We need to wait until the clock domain
> > stabilizes.
> > 
> > This issue seemed to have been caused by not waiting after frobbing
> > with the CPU bypass, it was unrelated to memory, but had a direct
> > impact, causing trouble. This was yet another X-File of the
> > imx-bootlets, sigh. The conclusion is, trying a semi-random delay
> > (there is delay after the EMI bypass change), the issue is fixed.
> > 
> > Another possible explanation is that we do not do the "simple memory
> > test" FSL does in their imx-bootlets (1000 R/W cycles to/from piece of
> > the memory, while also outputing something on the serial port). This
> > might have caused the similar delay in the imx-bootlets and therefore
> > they didn't need to add this explicitly.

Yes Stefano ... I meant this patch ... and the above explanation :-( This is all 
so messed up :-/

> > 
> > For now, this seems good fix enough, but to me, whole that memory
> > init code in imx-bootlets is completely flunked and it'd need deeper
> > investigation.
> > 
> > Signed-off-by: Marek Vasut <marex@denx.de>
> > Cc: Wolfgang Denk <wd@denx.de>
> > Cc: Detlev Zundel <dzu@denx.de>
> > Cc: Stefano Babic <sbabic@denx.de>
> > Cc: Fabio Estevam <festevam@gmail.com>
> > ---
> > 
> >  arch/arm/cpu/arm926ejs/mx28/spl_mem_init.c |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > V2: Change the description, this issue seemed to have been caused by not
> > 
> >     waiting after frobbing with the CPU bypass, it was unrelated to
> >     memory, but had a direct impact, causing trouble. This was yet
> >     another X-File of the imx-bootlets, sigh.
> > 
> > V3: Add more conspiracy theories into the commit message.
> > 
> > diff --git a/arch/arm/cpu/arm926ejs/mx28/spl_mem_init.c
> > b/arch/arm/cpu/arm926ejs/mx28/spl_mem_init.c index 0d13537..9fa5d29
> > 100644
> > --- a/arch/arm/cpu/arm926ejs/mx28/spl_mem_init.c
> > +++ b/arch/arm/cpu/arm926ejs/mx28/spl_mem_init.c
> > @@ -149,6 +149,8 @@ void mx28_mem_setup_cpu_and_hbus(void)
> > 
> >  	/* Disable CPU bypass */
> >  	writel(CLKCTRL_CLKSEQ_BYPASS_CPU,
> >  	
> >  		&clkctrl_regs->hw_clkctrl_clkseq_clr);
> > 
> > +
> > +	early_delay(15000);
> > 
> >  }
> 
> It is fine with me
> 
> Acked-by: Stefano Babic <sbabic@denx.de>
> 
> Best regards,
> Stefano Babic

Best regards,
Marek Vasut