linux-kernel - Re: [RFT PATCH v2 2/3] hwmon: (spd5118) Use spd5118 specific read/write operations

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Date: Tue, 18 Jun 2024 17:23:44 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Paul Menzel <pmenzel@...gen.mpg.de>, Armin Wolf <W_Armin@....de>
Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>,
 linux-kernel@...r.kernel.org, René Rebe
 <rene@...ctcode.de>, Thomas Weißschuh
 <linux@...ssschuh.net>, Stephen Horvath <s.horvath@...look.com.au>,
 Sasha Kozachuk <skozachuk@...gle.com>, John Hamrick <johnham@...gle.com>,
 Chris Sarra <chrissarra@...gle.com>, linux-hwmon@...r.kernel.org,
 Jean Delvare <jdelvare@...e.com>, Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [RFT PATCH v2 2/3] hwmon: (spd5118) Use spd5118 specific
 read/write operations

On 6/18/24 16:39, Paul Menzel wrote:
> [Cc: +Heiner]
> 
> 
> Dear Armin,
> 
> 
> Am 19.06.24 um 01:28 schrieb Armin Wolf:
>> Am 19.06.24 um 00:28 schrieb Wolfram Sang:
>>
>>>> to 86 degrees C. If that doesn't work, we'll be really out of luck
>>>> with that controller (or at least I don't have an idea what else to try).
>>>
>>> Try CCing Heiner Kallweit for ideas about the i801 controller.
> 
>> i am not Heiner Kallweit, but i found something interesting in
>> commit ba9ad2af7019 ("i2c: i801: Fix I2C Block Read on 8-Series/C220 and later").
>>
>> Basically, it seems that the i802 i2c controller indeed features a SPD write disable bit which blocks all writes for slave addresses 0x50-0x57.
>>
>> Does the i801 i2c controller driver print something like "SPD Write Disable is set" during boot?
> 
> Nice find. Yes, it does:
> 

Yes, definitely. I didn't have any recent datasheets, so I missed that flag.
Oh well :-(.

>      [    5.462605] i801_smbus 0000:00:1f.4: SPD Write Disable is set
>      [    5.468399] i801_smbus 0000:00:1f.4: SMBus using PCI interrupt
> 

Bummer. That explains the problem. It means that the BIOS effectively
blocks reading the eeprom on your system (because that would require writing
the page register), as well as changing temperature limits. That is really
annoying, but there is nothing we can do about it. Maybe the BIOS has a
configuration flag to enable or disable write protect, but I doubt it.

I'll drop this patch from the series.

Thanks,
Guenter