From 21d90aaee8d5c2a097ef41f1430d97661233ecc6 Mon Sep 17 00:00:00 2001
From: Hans de Goede <hdegoede@redhat.com>
Date: Thu, 24 Feb 2022 11:18:48 +0100
Subject: [PATCH] surface: surface3_power: Fix battery readings on batteries without a serial number
Git-commit: 21d90aaee8d5c2a097ef41f1430d97661233ecc6
Patch-mainline: v5.17-rc6
References: git-fixes

The battery on the 2nd hand Surface 3 which I recently bought appears to
not have a serial number programmed in. This results in any I2C reads from
the registers containing the serial number failing with an I2C NACK.

This was causing mshw0011_bix() to fail causing the battery readings to
not work at all.

Ignore EREMOTEIO (I2C NACK) errors when retrieving the serial number and
continue with an empty serial number to fix this.

Fixes: b1f81b496b0d ("platform/x86: surface3_power: MSHW0011 rev-eng implementation")
Buglink: https://github.com/linux-surface/linux-surface/issues/608
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Maximilian Luz <luzmaximilian@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20220224101848.7219-1-hdegoede@redhat.com
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/platform/surface/surface3_power.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/surface/surface3_power.c b/drivers/platform/surface/surface3_power.c
index abac3eec565e..444ec81ba02d 100644
--- a/drivers/platform/surface/surface3_power.c
+++ b/drivers/platform/surface/surface3_power.c
@@ -232,14 +232,21 @@ static int mshw0011_bix(struct mshw0011_data *cdata, struct bix *bix)
 	}
 	bix->last_full_charg_capacity = ret;
 
-	/* get serial number */
+	/*
+	 * Get serial number, on some devices (with unofficial replacement
+	 * battery?) reading any of the serial number range addresses gets
+	 * nacked in this case just leave the serial number empty.
+	 */
 	ret = i2c_smbus_read_i2c_block_data(client, MSHW0011_BAT0_REG_SERIAL_NO,
 					    sizeof(buf), buf);
-	if (ret != sizeof(buf)) {
+	if (ret == -EREMOTEIO) {
+		/* no serial number available */
+	} else if (ret != sizeof(buf)) {
 		dev_err(&client->dev, "Error reading serial no: %d\n", ret);
 		return ret;
+	} else {
+		snprintf(bix->serial, ARRAY_SIZE(bix->serial), "%3pE%6pE", buf + 7, buf);
 	}
-	snprintf(bix->serial, ARRAY_SIZE(bix->serial), "%3pE%6pE", buf + 7, buf);
 
 	/* get cycle count */
 	ret = i2c_smbus_read_word_data(client, MSHW0011_BAT0_REG_CYCLE_CNT);
-- 
2.31.1