[smartmontools-support] [PATCH v4] libata: Add hwmon support for SMART temperature sensors

[Christian Franke]

Douglas Gilbert wrote:
> On 2018-09-14 02:20 PM, James Bottomley wrote:
>> ...
>> Given that you're using scsi_execute and this would work on most SAS
>> drives as well as SATA ones, why not use the SAS mode pages and we'll
>> translate it to SATA in the existing libata-scsi SAT?
>
> Fetch the SCSI Temperature Log page [0xd] with the LOG SENSE SCSI 
> command.
> See sat5r01a.pdf chapter 10.3.8 for how that should be translated
> to ATA commands by libata and other SATLs.

Please note that SAT requires other access methods than the patch 
implements.

A comparison of ATA access methods for temperature:

1) ATA SMART Attribute 194 (from vendor specific SMART DATA):
- Provides: current temperature, possibly lifetime(?) min/max in various 
formats.
- Standards:
-- SMART READ DATA cmd: ATA-3 to ACS-3, no longer documented in ACS-4.
-- Attribute 194: "existing practice", not mentioned in any related 
standard,
- Supported by: virtually all HDD/SSD with temperature sensor.
- Used by: this patch, smartctl/smartd, most other disk monitoring tools.

2) ATA SCT Status (GP/SMART log address 0xe0):
- Provides: current temperature, power cycle min/max, lifetime min/max, 
over/under limit count.
- Standards: ATA-8 ACS or later.
- Supported by: various devices since ~2006, still unsupported by some 
recent devices.
- Used by: SAT-4 or later, smartctl 5.38+, ...?

3) ATA Temperature Statistics (GP log address 0x04, page 0x05):
- Provides current temperature, lifetime min/max, over/under limit time, ...
- Standards: ATA ACS-2 or later.
- Supported by: few devices since ~2010, still unsupported by many 
recent devices.
- Used by: SAT-3 or later, smartctl 5.42+, ...?

Interestingly SAT-4 adds the older SCT access method.

Christian