netdev - [PATCH v2 net-next 2/3] net: mvmdio: Avoid excessive sleeps in polled mode

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Message-Id: <20231204100811.2708884-3-tobias@waldekranz.com>
Date: Mon,  4 Dec 2023 11:08:10 +0100
From: Tobias Waldekranz <tobias@...dekranz.com>
To: davem@...emloft.net,
	kuba@...nel.org
Cc: andrew@...n.ch,
	gregory.clement@...tlin.com,
	sebastian.hesselbarth@...il.com,
	robh+dt@...nel.org,
	krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org,
	netdev@...r.kernel.org
Subject: [PATCH v2 net-next 2/3] net: mvmdio: Avoid excessive sleeps in polled mode

Before this change, when operating in polled mode, i.e. no IRQ is
available, every individual C45 access would be hit with a 150us sleep
after the bus access.

For example, on a board with a CN9130 SoC connected to an MV88X3310
PHY, a single C45 read would take around 165us:

    root@...ix:~$ mdio f212a600.mdio-mii mmd 4:1 bench 0xc003
    Performed 1000 reads in 165ms

By replacing the long sleep with a tighter poll loop, we observe a 10x
increase in bus throughput:

    root@...ix:~$ mdio f212a600.mdio-mii mmd 4:1 bench 0xc003
    Performed 1000 reads in 15ms

Signed-off-by: Tobias Waldekranz <tobias@...dekranz.com>
---
 drivers/net/ethernet/marvell/mvmdio.c | 53 ++++++++-------------------
 1 file changed, 16 insertions(+), 37 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvmdio.c b/drivers/net/ethernet/marvell/mvmdio.c
index 89f26402f8fb..5f66f779e56f 100644
--- a/drivers/net/ethernet/marvell/mvmdio.c
+++ b/drivers/net/ethernet/marvell/mvmdio.c
@@ -23,6 +23,7 @@
 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/kernel.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
@@ -58,11 +59,6 @@
  * - Armada 370       (Globalscale Mirabox):   41us to 43us (Polled)
  */
 #define MVMDIO_SMI_TIMEOUT		1000 /* 1000us = 1ms */
-#define MVMDIO_SMI_POLL_INTERVAL_MIN	45
-#define MVMDIO_SMI_POLL_INTERVAL_MAX	55
-
-#define MVMDIO_XSMI_POLL_INTERVAL_MIN	150
-#define MVMDIO_XSMI_POLL_INTERVAL_MAX	160
 
 struct orion_mdio_dev {
 	void __iomem *regs;
@@ -84,8 +80,6 @@ enum orion_mdio_bus_type {
 
 struct orion_mdio_ops {
 	int (*is_done)(struct orion_mdio_dev *);
-	unsigned int poll_interval_min;
-	unsigned int poll_interval_max;
 };
 
 /* Wait for the SMI unit to be ready for another operation
@@ -94,34 +88,23 @@ static int orion_mdio_wait_ready(const struct orion_mdio_ops *ops,
 				 struct mii_bus *bus)
 {
 	struct orion_mdio_dev *dev = bus->priv;
-	unsigned long timeout = usecs_to_jiffies(MVMDIO_SMI_TIMEOUT);
-	unsigned long end = jiffies + timeout;
-	int timedout = 0;
+	unsigned long timeout;
+	int done;
 
-	while (1) {
-	        if (ops->is_done(dev))
+	if (dev->err_interrupt <= 0) {
+		if (!read_poll_timeout_atomic(ops->is_done, done, done, 2,
+					      MVMDIO_SMI_TIMEOUT, false, dev))
+			return 0;
+	} else {
+		/* wait_event_timeout does not guarantee a delay of at
+		 * least one whole jiffie, so timeout must be no less
+		 * than two.
+		 */
+		timeout = max(usecs_to_jiffies(MVMDIO_SMI_TIMEOUT), 2);
+
+		if (wait_event_timeout(dev->smi_busy_wait,
+				       ops->is_done(dev), timeout))
 			return 0;
-	        else if (timedout)
-			break;
-
-	        if (dev->err_interrupt <= 0) {
-			usleep_range(ops->poll_interval_min,
-				     ops->poll_interval_max);
-
-			if (time_is_before_jiffies(end))
-				++timedout;
-	        } else {
-			/* wait_event_timeout does not guarantee a delay of at
-			 * least one whole jiffie, so timeout must be no less
-			 * than two.
-			 */
-			if (timeout < 2)
-				timeout = 2;
-			wait_event_timeout(dev->smi_busy_wait,
-				           ops->is_done(dev), timeout);
-
-			++timedout;
-	        }
 	}
 
 	dev_err(bus->parent, "Timeout: SMI busy for too long\n");
@@ -135,8 +118,6 @@ static int orion_mdio_smi_is_done(struct orion_mdio_dev *dev)
 
 static const struct orion_mdio_ops orion_mdio_smi_ops = {
 	.is_done = orion_mdio_smi_is_done,
-	.poll_interval_min = MVMDIO_SMI_POLL_INTERVAL_MIN,
-	.poll_interval_max = MVMDIO_SMI_POLL_INTERVAL_MAX,
 };
 
 static int orion_mdio_smi_read(struct mii_bus *bus, int mii_id,
@@ -194,8 +175,6 @@ static int orion_mdio_xsmi_is_done(struct orion_mdio_dev *dev)
 
 static const struct orion_mdio_ops orion_mdio_xsmi_ops = {
 	.is_done = orion_mdio_xsmi_is_done,
-	.poll_interval_min = MVMDIO_XSMI_POLL_INTERVAL_MIN,
-	.poll_interval_max = MVMDIO_XSMI_POLL_INTERVAL_MAX,
 };
 
 static int orion_mdio_xsmi_read_c45(struct mii_bus *bus, int mii_id,
-- 
2.34.1