linux-kernel - [PATCH] net: mdiobus: Prevent spike on MDIO bus reset signal

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Message-Id: <20210126073337.20393-1-mike.looijmans@topic.nl>
Date:   Tue, 26 Jan 2021 08:33:37 +0100
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     netdev@...r.kernel.org
Cc:     Mike Looijmans <mike.looijmans@...ic.nl>,
        Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] net: mdiobus: Prevent spike on MDIO bus reset signal

The mdio_bus reset code first de-asserted the reset by allocating with
GPIOD_OUT_LOW, then asserted and de-asserted again. In other words, if
the reset signal defaulted to asserted, there'd be a short "spike"
before the reset.

Instead, directly assert the reset signal using GPIOD_OUT_HIGH, this
removes the spike and also removes a line of code since the signal
is already high.

Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>

---

 drivers/net/phy/mdio_bus.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 2b42e46066b4..34e98ae75110 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -543,8 +543,8 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 	mutex_init(&bus->mdio_lock);
 	mutex_init(&bus->shared_lock);
 
-	/* de-assert bus level PHY GPIO reset */
-	gpiod = devm_gpiod_get_optional(&bus->dev, "reset", GPIOD_OUT_LOW);
+	/* assert bus level PHY GPIO reset */
+	gpiod = devm_gpiod_get_optional(&bus->dev, "reset", GPIOD_OUT_HIGH);
 	if (IS_ERR(gpiod)) {
 		err = dev_err_probe(&bus->dev, PTR_ERR(gpiod),
 				    "mii_bus %s couldn't get reset GPIO\n",
@@ -553,8 +553,6 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 		return err;
 	} else	if (gpiod) {
 		bus->reset_gpiod = gpiod;
-
-		gpiod_set_value_cansleep(gpiod, 1);
 		fsleep(bus->reset_delay_us);
 		gpiod_set_value_cansleep(gpiod, 0);
 		if (bus->reset_post_delay_us > 0)
-- 
2.17.1