linux-kernel - [PATCH 2/2] i2c: i801: don't instantiate spd5118 if SPD Write Disable is set

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Message-Id: <20250424-for-upstream-i801-spd5118-no-instantiate-v1-2-627398268a1f@canonical.com>
Date: Thu, 24 Apr 2025 11:35:44 +0800
From: "Yo-Jung (Leo) Lin" <leo.lin@...onical.com>
To: Jean Delvare <jdelvare@...e.com>, Andi Shyti <andi.shyti@...nel.org>, 
 Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Guenter Roeck <linux@...ck-us.net>, 
 "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.com>, 
 linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org, 
 "Yo-Jung Lin (Leo)" <leo.lin@...onical.com>
Subject: [PATCH 2/2] i2c: i801: don't instantiate spd5118 if SPD Write
 Disable is set

If SPD Write Disable bit in the SMBus is enabled, writing data to
addresses from 0x50 to 0x57 is forbidden. This may lead to the
following issues for spd5118 device:

  1) Writes to the sensor hwmon sysfs attributes will always result
     in ENXIO.

  2) System-wide resume, errors may occur during regcache sync,
     resulting in the following error messages:

     kernel: spd5118 1-0050: Failed to write b = 0: -6
     kernel: spd5118 1-0050: PM: dpm_run_callback(): spd5118_resume [spd5118] returns -6
     kernel: spd5118 1-0050: PM: failed to resume async: error -6

  3) nvmem won't be usable, because writing to the page selector becomes
     impossible.

Also, spd5118 from some manufacturers may set the page to a value != 0
after a sensor reset. This will make the sensor not functional unless
its MR11 register can be changed, which is impossible due to writes being
disabled.

To address these issues, don't instantiate it at all if SPD Write Disable
bit is set.

Signed-off-by: Yo-Jung (Leo) Lin <leo.lin@...onical.com>
---
 drivers/i2c/i2c-smbus.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 97e833895dd7..cb7ef6a7a174 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -378,6 +378,7 @@ void i2c_register_spd(struct i2c_adapter *adap, bool write_disabled)
 	u16 handle;
 	u8 common_mem_type = 0x0, mem_type;
 	u64 mem_size;
+	bool scan_needed = true;
 	const char *name;
 
 	while ((handle = dmi_memdev_handle(slot_count)) != 0xffff) {
@@ -438,6 +439,7 @@ void i2c_register_spd(struct i2c_adapter *adap, bool write_disabled)
 	case 0x22:	/* DDR5 */
 	case 0x23:	/* LPDDR5 */
 		name = "spd5118";
+		scan_needed = !write_disabled;
 		break;
 	default:
 		dev_info(&adap->dev,
@@ -461,6 +463,9 @@ void i2c_register_spd(struct i2c_adapter *adap, bool write_disabled)
 		addr_list[0] = 0x50 + n;
 		addr_list[1] = I2C_CLIENT_END;
 
+		if (!scan_needed)
+			continue;
+
 		if (!IS_ERR(i2c_new_scanned_device(adap, &info, addr_list, NULL))) {
 			dev_info(&adap->dev,
 				 "Successfully instantiated SPD at 0x%hx\n",

-- 
2.43.0