linux-kernel - [PATCH 5.10 01/57] net: dsa: microchip: Adjust reset release timing to match reference reset circuit

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Date:   Fri,  5 Feb 2021 15:06:27 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
        Marek Vasut <marex@...x.de>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Paul Barker <pbarker@...sulko.com>,
        Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH 5.10 01/57] net: dsa: microchip: Adjust reset release timing to match reference reset circuit

From: Marek Vasut <marex@...x.de>

commit 1c45ba93d34cd6af75228f34d0675200c81738b5 upstream.

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@...il.com>
Signed-off-by: Marek Vasut <marex@...x.de>
Cc: Michael Grzeschik <m.grzeschik@...gutronix.de>
Reviewed-by: Paul Barker <pbarker@...sulko.com>
Reviewed-by: Andrew Lunn <andrew@...n.ch>
Link: https://lore.kernel.org/r/20210120030502.617185-1-marex@denx.de
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/dsa/microchip/ksz_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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);
-- 
2.30.0