linux-kernel - [PATCH v2 2/2] hwmon: (pmbus/bpa-rs600) Add workaround for incorrect Pin max

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Date:   Thu, 12 Aug 2021 13:40:00 +1200
From:   Chris Packham <chris.packham@...iedtelesis.co.nz>
To:     linux@...ck-us.net, jdelvare@...e.com
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Packham <chris.packham@...iedtelesis.co.nz>
Subject: [PATCH v2 2/2] hwmon: (pmbus/bpa-rs600) Add workaround for incorrect Pin max

BPD-RS600 modules running firmware v5.70 misreport the MFR_PIN_MAX.
The indicate a maximum of 1640W instead of 700W. Detect the invalid
reading and return a sensible value instead.

Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
---

Notes:
    Changes in v2:
    - Add comments for magic values

 drivers/hwmon/pmbus/bpa-rs600.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/hwmon/pmbus/bpa-rs600.c b/drivers/hwmon/pmbus/bpa-rs600.c
index 84dee86399cb..f2d4e378a775 100644
--- a/drivers/hwmon/pmbus/bpa-rs600.c
+++ b/drivers/hwmon/pmbus/bpa-rs600.c
@@ -65,6 +65,26 @@ static int bpa_rs600_read_vin(struct i2c_client *client)
 	return ret;
 }
 
+/*
+ * Firmware V5.70 incorrectly reports 1640W for MFR_PIN_MAX.
+ * Deal with this by returning a sensible value.
+ */
+static int bpa_rs600_read_pin_max(struct i2c_client *client)
+{
+	int ret;
+
+	ret = pmbus_read_word_data(client, 0, 0xff, PMBUS_MFR_PIN_MAX);
+	if (ret < 0)
+		return ret;
+
+	/* Detect invalid 1640W (linear encoding) */
+	if (ret == 0x0b34)
+		/* Report 700W (linear encoding) */
+		return 0x095e;
+
+	return ret;
+}
+
 static int bpa_rs600_read_word_data(struct i2c_client *client, int page, int phase, int reg)
 {
 	int ret;
@@ -91,6 +111,9 @@ static int bpa_rs600_read_word_data(struct i2c_client *client, int page, int pha
 	case PMBUS_READ_VIN:
 		ret = bpa_rs600_read_vin(client);
 		break;
+	case PMBUS_MFR_PIN_MAX:
+		ret = bpa_rs600_read_pin_max(client);
+		break;
 	default:
 		if (reg >= PMBUS_VIRT_BASE)
 			ret = -ENXIO;
-- 
2.32.0