linux-kernel - [PATCH] hwmon: max34451: Workaround for lost page

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Message-ID: <20250401220850.3189582-1-william@wkennington.com>
Date: Tue,  1 Apr 2025 15:08:50 -0700
From: "William A. Kennington III" <william@...nnington.com>
To: Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>
Cc: linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	openbmc@...ts.ozlabs.org,
	"William A. Kennington III" <william@...nnington.com>
Subject: [PATCH] hwmon: max34451: Workaround for lost page

When requesting new pages from the max34451 we sometimes see that the
firmware doesn't update the page on the max34451 side fast enough. This
results in the kernel receiving data for a different page than what it
expects.

To remedy this, the manufacturer recommends we wait 50-100us until
the firmware should be ready with the new page.

Signed-off-by: William A. Kennington III <william@...nnington.com>
---
 drivers/hwmon/pmbus/max34440.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/hwmon/pmbus/max34440.c b/drivers/hwmon/pmbus/max34440.c
index c9dda33831ff..ac3a26f7cff3 100644
--- a/drivers/hwmon/pmbus/max34440.c
+++ b/drivers/hwmon/pmbus/max34440.c
@@ -12,6 +12,7 @@
 #include <linux/init.h>
 #include <linux/err.h>
 #include <linux/i2c.h>
+#include <linux/delay.h>
 #include "pmbus.h"
 
 enum chips { max34440, max34441, max34446, max34451, max34460, max34461 };
@@ -241,6 +242,12 @@ static int max34451_set_supported_funcs(struct i2c_client *client,
 		if (rv < 0)
 			return rv;
 
+		/* Firmware is sometimes not ready if we try and read the
+		 * data from the page immediately after setting. Maxim
+		 * recommends 50-100us delay.
+		 */
+		fsleep(50);
+
 		rv = i2c_smbus_read_word_data(client,
 					      MAX34451_MFR_CHANNEL_CONFIG);
 		if (rv < 0)
-- 
2.49.0.472.ge94155a9ec-goog