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.
> Include this delay in the regulator startup delay - effectively
> treating the reset as a "supply stable" indicator.
>
> This can not be modelled as a delay in the KSZ8851 driver since the
> reset generation is board specific - if the RSTN pin had been wired to
> a GPIO, reset could be released earlier via the already provided support
> in the KSZ8851 driver.
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
> ---
> arch/arm/boot/dts/omap4-sdp.dts | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm/boot/dts/omap4-sdp.dts b/arch/arm/boot/dts/omap4-sdp.dts
> index 0831a2bf6cec..57acf3a8b8a1 100644
> --- a/arch/arm/boot/dts/omap4-sdp.dts
> +++ b/arch/arm/boot/dts/omap4-sdp.dts
> @@ -33,6 +33,7 @@
> gpio = <&gpio2 16 GPIO_ACTIVE_HIGH>; /* gpio line 48 */
> enable-active-high;
> regulator-boot-on;
> + startup-delay-us = <25000>;
> };
>
> vbat: fixedregulator-vbat {
>
- Péter
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