Re: [PATCH 0/2] i2c: i801: Detect SPD Write Disable and expose as adapter quirk

["Mark Pearson" <mpearson@squebb.ca>]

Hi Tinsae,

On Sat, Feb 21, 2026, at 4:57 AM, TINSAE TADESSE wrote:
> On Thu, Feb 5, 2026 at 1:29 PM Tinsae Tadesse
> <tinsaetadesse2015@gmail.com> wrote:
>>
>> Hi I2C and HWMON maintainers,
>>
>> Intel i801 SMBus controllers feature a "SPD Write Disable" bit
>> in the SMBHSTCFG register. When set by firmware, the hardware
>> silently blocks all write transactions to the SPD EEPROM
>> address range (0x50-0x57) while allowing reads to succeed.
>>
>> This creates a significant issue for the spd5118 hwmon driver.
>> The SPD5118 requires write access for switching between
>> register pages to read temperature data, and for cache
>> synchronization during suspend/resume. When SPD Write Disable
>> is set and the spd5118 driver attempts write transactions, the
>> bus will generate a storm of SMBus DEV_ERR messages.
>>
>> This patch series proposes a generic solution by:
>> 1. Introducing a new adapter quirk flag in include/linux/i2c.h
>> to communicate this hardware restriction.
>> 2. Modifying drivers/i2c/i2c-i801.c to detect the SPD Write
>> Disable bit and set the quirk flag.
>> 3. Modifying drivers/hwmon/spd5118.c to check for this quirk
>> during probe and fail cleanly, as write access is mandatory.
>>
>> By using this mechanism, we avoid embedding device-specific
>> policies in the controller driver and provide client drivers
>> with the necessary information to make an informed decision.
>>
>> Tinsae Tadesse (2):
>>   i2c: i801: Detect SPD Write Disable and expose as adapter quirk
>>   hwmon: spd5118: Fail probe if SPD writes are disabled
>>
>>  drivers/hwmon/spd5118.c       | 15 +++++++++++++++
>>  drivers/i2c/busses/i2c-i801.c | 16 +++++++++++++++-
>>  include/linux/i2c.h           |  3 +++
>>  3 files changed, 33 insertions(+), 1 deletion(-)
>>
>> --
>> 2.52.0
>>
>

I'm hitting a very similar problem on all the Lenovo 2026 Linux certified platforms.
Your patch is great, and I wanted to add a tested-by tag to say it fixed the issue for me, but it doesn't quite unfortunately.

I added this change (hack?) in i2c-smbus.c to take advantage of your changes and fix the issue that I'm seeing:

 void i2c_register_spd_write_enable(struct i2c_adapter *adap)
 {
-       i2c_register_spd(adap, false);
+       if (adap->quirks && adap->quirks->flags & I2C_AQ_SPD_WRITE_DISABLED)
+               i2c_register_spd(adap, true);
+       else
+               i2c_register_spd(adap, false);
 }

What do you think? Any side effects or impacts you can foresee based on your testing?

Maintainers - would love your opinion too. I suspect this may become a common issue.

Mark