net: dsa: microchip: Adjust reset release timing to match reference reset circuit

KSZ8794CNX datasheet section 8.0 RESET CIRCUIT describes recommended
circuit for interfacing with CPU/FPGA reset consisting of 10k pullup
resistor and 10uF capacitor to ground. This circuit takes ~100 ms to
rise enough to release the reset.

For maximum supply voltage VDDIO=3.3V VIH=2.0V R=10kR C=10uF that is
                    VDDIO - VIH
  t = R * C * -ln( ------------- ) = 10000*0.00001*-(-0.93)=0.093 s
                       VDDIO
so we need ~95 ms for the reset to really de-assert, and then the
original 100us for the switch itself to come out of reset. Simply
msleep() for 100 ms which fits the constraint with a bit of extra
space.

Fixes: 5b797980908a ("net: dsa: microchip: Implement recommended reset timing")
Reviewed-by: Florian Fainelli <[email protected]>
Signed-off-by: Marek Vasut <[email protected]>
Cc: Michael Grzeschik <[email protected]>
Reviewed-by: Paul Barker <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index 489963664443..389abfd27770 100644
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -400,7 +400,7 @@ int ksz_switch_register(struct ksz_device *dev,
 		gpiod_set_value_cansleep(dev->reset_gpio, 1);
 		usleep_range(10000, 12000);
 		gpiod_set_value_cansleep(dev->reset_gpio, 0);
-		usleep_range(100, 1000);
+		msleep(100);
 	}
 
 	mutex_init(&dev->dev_mutex);