netdev - [PATCH] net: sfp: workaround GPIO input signals bounce

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Date:   Tue, 13 Sep 2022 10:43:38 +0300
From:   Baruch Siach <baruch@...s.co.il>
To:     Russell King <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Baruch Siach <baruch.siach@...lu.com>
Subject: [PATCH] net: sfp: workaround GPIO input signals bounce

From: Baruch Siach <baruch.siach@...lu.com>

Add a trivial debounce to avoid miss of state changes when there is no
proper hardware debounce on the input signals. Otherwise a GPIO might
randomly indicate high level when the signal is actually going down,
and vice versa.

This fixes observed miss of link up event when LOS signal goes down on
Armada 8040 based system with an optical SFP module.

Signed-off-by: Baruch Siach <baruch.siach@...lu.com>
---
 drivers/net/phy/sfp.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index 63f90fe9a4d2..ce6565872f54 100644
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -313,7 +313,9 @@ static unsigned long poll_jiffies;
 static unsigned int sfp_gpio_get_state(struct sfp *sfp)
 {
 	unsigned int i, state, v;
+	int repeat = 10;
 
+again:
 	for (i = state = 0; i < GPIO_MAX; i++) {
 		if (gpio_flags[i] != GPIOD_IN || !sfp->gpio[i])
 			continue;
@@ -323,6 +325,15 @@ static unsigned int sfp_gpio_get_state(struct sfp *sfp)
 			state |= BIT(i);
 	}
 
+	/* Trivial debounce. When no state change is detected, wait for up to
+	 * a limited bound time interval for the signal state to settle.
+	 */
+	if (state == sfp->state && repeat > 0) {
+		udelay(10);
+		repeat--;
+		goto again;
+	}
+
 	return state;
 }
 
-- 
2.35.1