Re: [EXTERNAL] Re: Potential issue with smb word operations for tmp461 device in tmp401 driver

["Wilson, David T. (GSFC-5870)" <david.wilson@nasa.gov>]

Guenter,

I've tried testing the patch by checking out the most recent commit's version for tmp401.c and applying the patch. However, the temperature values seem to be to low <1000 for each read.

If I'm understanding the driver code correctly, I believe there's two places of interest that might explain the low values
1. In tmp401_update_device_reg16, the final assignment to data->temp[j][i] overrides the patch's assignment to data->temp[j][i] in the tmp461 branch
2. In SENSOR_DEVICE_ATTR_2_RW, the temp2_offset is at (6, 1), but the newly added LSB array does not contain the LSB address at (6, 1)

Regarding your most recent email, I will try the lm90 by changing the driver tree entry to "ti,tmp451" and I'll let you know if that works for me.

Thanks,
David

From: Guenter Roeck <groeck7@gmail.com> on behalf of Guenter Roeck <linux@roeck-us.net>
Sent: Tuesday, October 19, 2021 12:56 AM
To: Wilson, David T. (GSFC-5870) <david.wilson@nasa.gov>
Cc: linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>; linux-hwmon@vger.kernel.org <linux-hwmon@vger.kernel.org>
Subject: [EXTERNAL] 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://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fe2e.ti.com%2Fsupport%2Fsensors-group%2Fsensors%2Ff%2Fsensors-forum%2F1044935%2Ftmp461-linux-driver-support-and-16-bit-temperature-register-reads&amp;data=04%7C01%7Cdavid.wilson%40nasa.gov%7C2bf9c7234976452dd4a808d992bcc836%7C7005d45845be48ae8140d43da96dd17b%7C0%7C0%7C637702161780144423%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=JerajTZnSdtQgGlVrfm3IOLNpQcoVKeg5haNU8h1aDs%3D&amp;reserved=0).
> 
> 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