[U-Boot] [PATCH] mx23: Put back RAM voltage level to its original value

[Marek Vasut <marex@denx.de>]

Dear Fabio Estevam,

> On Fri, Apr 26, 2013 at 3:16 PM, Marek Vasut <marex@denx.de> wrote:
> > Dear Fabio Estevam,
> > 
> >> On Fri, Apr 26, 2013 at 1:24 PM, Eric B?nard <eric@eukrea.com> wrote:
> >> > what are the values of these levels (previous one and new one) in mV ?
> >> 
> >> 0x10 ==> 2.5V
> >> 0x12 ==> 2.6V
> >> 
> >> 46v32m16
> > 
> > Eh? What's this code above?
> 
> It is the DDR part number on mx23evk.
> 
> >> says that VDD is : 2.5V +/- 0.2V, so 2.6V is a valid supply
> >> voltage.
> >> 
> >> Not sure why 2.5V fails though.
> > 
> > http://s8.postimg.org/dn7jhntut/imx233_olinuxino_maxi_2_5_V_rising.jpg
> > check this, this is as much as I got from tsvetan so far, it's the
> > VDDMEM ramping. I dunno what's that weird drop before it starts going
> > from 1V5 to 2V5, but it's
> 
> Why 1.5V? The VDDMEM reset value is 1.7V.

Some voltage drop, that's no problem.

> > strange at best and I don't like it. I think that's also the source of
> > our problems, the DRAM suffers undervolt and quickly afterwards is
> > configured for regular operation ... I'd say check
> > mx23_mem_setup_vddmem() and inspect the result with a scope. I think we
> > need some slow ramping function like mxs_power_set_vddx().
> 
> Ok, but can we have this patch applied and do this investigation in
> parallel?
> 
> At least we could have U-boot usable on mx23 again.

I'd say try one more thing -- use a different PSU. I suspect the powerblock on 
olinuxino is cheap crap and the stability of the DRAM depends on the PSU too. 
After that, yes, we can have it in.

Best regards,
Marek Vasut