netdev - [PATCH v2] net: sfp: workaround GPIO input signals bounce

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Message-Id: <931ac53e9d6421f71f776190b2039abaa69f7d43.1663133795.git.baruch@tkos.co.il>
Date:   Wed, 14 Sep 2022 08:36:35 +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 v2] 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>
---
v2:
  Skip delay in the polling case (RMK)
---
 drivers/net/phy/sfp.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index 63f90fe9a4d2..b0ba144c9633 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 +325,16 @@ static unsigned int sfp_gpio_get_state(struct sfp *sfp)
 			state |= BIT(i);
 	}
 
+	/* Trivial debounce for the interrupt case. 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 && !sfp->need_poll && repeat > 0) {
+		udelay(10);
+		repeat--;
+		goto again;
+	}
+
 	return state;
 }
 
-- 
2.35.1