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 <f.fainelli@gmail.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Michael Grzeschik <m.grzeschik@pengutronix.de>
Reviewed-by: Paul Barker <pbarker@konsulko.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20210120030502.617185-1-marex@denx.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index 4899636644438f3c3d61573ee7343bd2656488bf..389abfd277702968558d435f482c21c2ec4b30ac 100644 (file)
--- 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);