Re: [PATCH] Fix OMAP4430 SDP Ethernet startup

[Tony Lindgren <tony@atomide.com>]

* Russell King - ARM Linux <linux@armlinux.org.uk> [181207 13:58]:
> On Fri, Dec 07, 2018 at 03:40:13PM +0200, Peter Ujfalusi wrote:
> > Russell,
> > 
> > On 07/12/2018 14.52, Russell King - ARM Linux wrote:
> > > It was noticed that unbinding and rebinding the KSZ8851 ethernet
> > > resulted in the driver reporting "failed to read device ID" at probe.
> > > Probing the reset line with a 'scope while repeatedly attempting to
> > > bind the driver in a shell loop revealed that the KSZ8851 RSTN pin is
> > > constantly held at zero, meaning the device is held in reset, and
> > > does not respond on the SPI bus.
> > > 
> > > Experimentation with the startup delay on the regulator set to 50ms
> > > shows that the reset is positively released after 20ms.
> > > 
> > > Schematics for this board are not available, and the traces are buried
> > > in the inner layers of the board which makes tracing where the RSTN pin
> > > extremely difficult.  We can only guess that the RSTN pin is wired to a
> > > reset generator chip driven off the ethernet supply, which fits the
> > > observed behaviour.
> > 
> > Based on the schematics of the Blaze device (which should be very close
> > to SDP4430):
> > 
> > TPS22902YFPR is used as the regulator switch (gpio48 controlled)
> > The VOUT is routed to  TPS3808G01DBV (SCH Note: Threshold set at 90%.
> > Vsense: 0.405V).
> > 
> > According to the TPS3808 data sheet the RESET delay time when Ct is open
> > (this is the case in the schema): MIN/TYP/MAX: 12/20/28 ms.
> > 
> > The 20ms you are seeing confirms this setup.
> 
> Thanks for the confirmation and information.  The Blaze schematics
> are also unavailable afaics.

Thanks applying into omap-for-v4.20/fixes with updated notes
from Peter for the wiring.

Regards,

Tony