In the past, several attempts have been made to add support for reporting SCSI/[S]ATA drive temperatures to the Linux kernel. This is desirable to have a means to report drive temperatures to userspace without root privileges and in a standard format, but also to be able to tie reported temperatures with the thermal subsystem. The most recent attempt was [1] by Linus Walleij. It went through a total of seven iterations. At the end, it was rejected for a number of reasons; see the provided link for details. This implementation resides in the SCSI core. It originally resided in libata but was moved to SCSI per maintainer request, where it was ultimately rejected. The feedback on this approach suggests to use the SCSI Temperature log page [0x0d] as means to access drive temperature information. It is unknown if this is implemented in any real SCSI drive. The feedback also suggests to obtain temperature from ATA drives, convert it into the SCSI temperature log page in libata-scsi, and to use that information in a hardware monitoring driver. The format and method to do this is documented in [3]. This is not currently implemented in the Linux kernel. An earlier submission of a driver to report SCSI/SATA drive temperatures was made back in 2009 by Constantin Baranov [2]. This submission resides in the hardware monitoring subsystem. It does not rely on changes in the SCSI subsystem or in libata-scsi. Instead, it registers itself with the SCSI subsystem using scsi_register_interface(). It was rejected primarily because it executes ATA passthrough commands without verification that it is actually connected to an ATA drive. Both submissions use SMART attributes to read drive temperature information. [1] also tries to identify temperature limits from those attributes. Unfortunately, SMART attributes are not well defined, resulting in relative complex code trying to identify the exact format of the reported data. With the available information and feedback, we can make a number of observations and conclusions. a) Using available (S)ATA drive temperature information and convert it to a SCSI log page is an interesting idea. On the downside, it would add a substantial amount of complexity to libata-scsi. The code would either have to be optional, or it would have to be built into the kernel even if it is never used on a given system. Without access to SCSI drives supporting this feature, it would be all but impossible to test the code against such a drive. It would neither be possible to test correctness of the code in libata-scsi nor in the driver using that information. Overall it would be much easier and much less risky to implement such code on the receiving side (ie in a driver reporting the temperatures) instead of trying to convert the information from one format to another first. In summary, it is neither practical nor feasible. On top of that, there is no guarantee that code implementing this functionality would ever be accepted into the kernel for this very reason. b) The code needed to read and analyze SCSI temperature log pages is quite complex (see smartmontools [5]). There is no existing support code in the Linux kernel; such code would have to be written. This makes the approach discussed in a) even more risky and less practical. c) Overall, any attempt to report temperature information for anything but SATA drives in the kernel is not practical due to the complexity involved, and due to the inability to test the resulting code with non-SATA drives. d) Using SMART data for anything but basic temperature reporting is not really feasible due to the lack of standardization. Any attempt to do this would add a substantial amount of code, ambiguity, and risk. This submission implements a driver to report the temperature of SATA drives through the hardware monitoring subsystem. It is implemented as stand-alone driver in the hardware monitoring subsystem. The driver uses the mechanism from submission [1] to register with the SCSI subsystem. By using this mechanism, changes in the SCSI or ATA subsystems are not required. To reduce risk and complexity, it only instantiates after reliably validating that it is connected to a SATA drive. It does not attempt to report the temperature of non-SATA drives. The driver uses the SCT Command Transport feature set as specified in ATA8-ACS [4] to read and report the temperature as well as temperature limits and lowest/highest temperature information (if available) for SATA drives. If a drive does not support SCT Command Transport, the driver attempts to access a limited set of well known SMART attributes to read the drive temperature. In that case, only the current drive temperature is reported. --- References: [1] https://patchwork.kernel.org/patch/10688021/ [2] https://lore.kernel.org/lkml/20090913040104.ab1d0b69.const@xxxxxxxx/ [3] http://www.t10.org/cgi-bin/ac.pl?t=f&f=sat5r02.pdf Information technology - SCSI / ATA Translation - 5 (SAT-5), section 10.3.8 (Temperature log page). [4] http://www.t13.org/documents/uploadeddocuments/docs2008/d1699r6a-ata8-acs.pdf ANS T13/1699-D "Information technology - AT Attachment 8 - ATA/ATAPI Command Set (ATA8-ACS)" [5] https://github.com/mirror/smartmontools.git
