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[0/2] i2c: i801: Don't instantiate spd5118 under SPD Write Disable

Message ID 20250424-for-upstream-i801-spd5118-no-instantiate-v1-0-627398268a1f@canonical.com
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Series i2c: i801: Don't instantiate spd5118 under SPD Write Disable | expand

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Yo-Jung (Leo) Lin April 24, 2025, 3:35 a.m. UTC 
On some PC platforms, the BIOS may enable i801's SPD Write Disable bit and
forbid writes to certain SMBus addresses. For the i801 family those addresses
are 0x50 to 0x57[1], where the spd5118 sensors are usually probed.

The write-disabling bit will make sensor functions related to writes and
nvmem access unusable.

Also, the driver is unable to sync back values from regcache to the sensors
during resume, leading to resume failure. This has been observed on multiple
existing PC platforms from Dell and HP.

Furthermore, for the sensors from certain manufacturers, after a reset they
may need to select page value to 0 before sensor values can be read. Not
being able to write to the registers renders the temperature reading
unusable. See discussion in [2].

To address these issues, do not instantiate spd5118 if SPD Write Disable
bit is set.

[1] 18.1.16 HOSTC—Host Configuration Register (SMBus—D31:F3),
    Intel 8 Series/C220 Series Chipset Family Platform Controller Hub(PCH)

[2] https://lore.kernel.org/all/acf31929-5d13-4fc5-b370-ab7fc5062455@roeck-us.net/

Signed-off-by: Yo-Jung Lin (Leo) <leo.lin@canonical.com>
---
Yo-Jung (Leo) Lin (2):
      i2c: smbus: pass write disabling bit to spd instantiating function
      i2c: i801: don't instantiate spd5118 if SPD Write Disable is set

 drivers/i2c/busses/i2c-i801.c  | 6 ++++--
 drivers/i2c/busses/i2c-piix4.c | 2 +-
 drivers/i2c/i2c-smbus.c        | 7 ++++++-
 include/linux/i2c-smbus.h      | 4 ++--
 4 files changed, 13 insertions(+), 6 deletions(-)
---
base-commit: b425262c07a6a643ebeed91046e161e20b944164
change-id: 20250423-for-upstream-i801-spd5118-no-instantiate-3b52d489e7a6

Best regards,