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

[Marek Vasut]

On Monday, November 16, 2015 at 08:47:38 PM, Michael Heimpold wrote:
> Hi Marek,

Hi!

> 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 at heimpold.de>
> > > Cc: Marek Vasut <marex at denx.de>
> > > Cc: Otavio Salvador <otavio at ossystems.com.br>
> > > Cc: Fabio Estevam <fabio.estevam at 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...

Heh, nice. Thanks!

Best regards,
Marek Vasut