Re: [PATCH] Fix OMAP4430 SDP Ethernet startup

[Russell King - ARM Linux <linux@armlinux.org.uk>]

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.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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