[U-Boot] [PATCH] ARM: mxs: fix VDDD brownout setting

[Michael Heimpold <mhei@heimpold.de>]

Hi Marek,

Am Monday 16 November 2015, 12:01:36 schrieben Sie:
> On Sunday, November 15, 2015 at 10:47:12 PM, Michael Heimpold wrote:
> > At the moment, the desired brownout is at 1.0V. However,
> > this setting cannot be realized by hardware since we have
> > only 3 bits to represent the voltage difference from the
> > target value.
> > 
> > Target value is 1500 mV, brownout target is 1000 mV,
> > voltage steps are 25 mV.
> > 
> > Register content calculation:
> >   (1500 [mV] - 1000 [mV]) / 25 [mV] = 20 (decimal) = 0x14
> >   
> >   Register takes only 3 bits, that is 0x4.
> > 
> > But 0x4 * 25 [mV] = 100 [mV], that means that actual
> > brownout level is 1500 [mV] - 100 [mV] = 1.4 V.
> > 
> > Minimum possible BO level is
> > 
> >   1500 [mV] - 0x7 * 25 [mV] = 1315 [mV].
> > 
> > So lets use this value as desired BO value (which is
> > also the same as FSL bootlets use).
> > 
> > Signed-off-by: Michael Heimpold <mhei@heimpold.de>
> > Cc: Marek Vasut <marex@denx.de>
> > Cc: Otavio Salvador <otavio@ossystems.com.br>
> > Cc: Fabio Estevam <fabio.estevam@freescale.com>
> 
> Uh, nice find. How did you find it?

I was investigating a boot stall with I2SE's Duckbill devices and since we're
about to switch from FSL bootlets to U-Boot, I compared the register
settings. Then I stumbled about the comment and wondered whether
1.0V BO level makes sense for 1.5V target voltage...

Best regards,
Michael Heimpold

> 
> Acked-by: Marek Vasut <marex@denx.de>
> 
> Best regards,
> Marek Vasut