linux-kernel - Re: Potential issue with smb word operations for tmp461 device in tmp401 driver

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Date:   Mon, 18 Oct 2021 21:56:09 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Wilson, David T. (GSFC-5870)" <david.wilson@...a.gov>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>
Subject: Re: Potential issue with smb word operations for tmp461 device in
 tmp401 driver

David,

On 10/15/21 10:43 AM, Wilson, David T. (GSFC-5870) wrote:
> Hi,
> 
> I am reporting what I believe is a potential issue in the tmp401 driver for the tmp461 device specifically. I am new to reporting issues, so I apologize in advance if I've provided insufficient information for an issue report.
> 
> The problem I'm encountering is that when I use the tmp401 linux driver to read temperature values from the tmp461, all of the read temperature values end with 996 (e.g. 33996, 38996, etc...).
> 
> Looking further into the tmp401 commit messages, I see that the driver was changed to use smb word operations instead of separate byte operations. Although the other supported devices (i.e. tmp432, etc...) are noted to support 16-bit read operations in their respective datasheets, I see no indications of 16-bit read support in the tmp461 datasheet, which is supported by my inquiry in the TI forums (https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1044935/tmp461-linux-driver-support-and-16-bit-temperature-register-reads).
> 
> Reverting the driver to the commit before the smb word change, I am then able to read temperature values that do not end only with 996. As a result, I believe that the tmp461 support may be partially broken by the switch to smb word operations.
> 

can you try to instantiate the lm90 driver (instead of the tmp401 driver)
and let me know if it works for you ? If your system uses devicetree,
you might have to select "ti,tmp451" instead of "ti,tmp461".

Thanks,
Guenter