Re: [PATCH 1/1] hwmon: Driver for temperature sensors on SATA drives

[Guenter Roeck <linux@roeck-us.net>]

On 12/12/19 3:21 PM, Martin K. Petersen wrote:
> 
> Linus,
> 
>> It's a nice addition with the SCT command, I never figured that part
>> out. Also nice how you register the scsi class interface I never saw
>> that before, it makes it a very neat plug-in.
> 
> Yep, I agree that the patch looks pretty good in general. There are just
> a few wrinkles in the detection heuristics I would like to tweak. More
> on that later.
> 
> Yesterday I added support for the SCSI temperature log page and am
> working through some kinks wrt. making this work for USB as well.
> 
>> When I read the comments from the previous thread I got the impression
>> the SCSI people wanted me to use something like the SCT transport and
>> the hook in the SMART thing in the libata back-end specifically for
>> [S]ATA in response to the SCT read log command.
> 
> Our recommendation was for libata-scsi.c to export the SCSI temperature
> log page, just like we do for all the other ATA parameters.
> 
> However, in tinkering with this the last couple of days, I find myself
> torn on the subject. For two reasons. First of all, there is no 1:1
> sensor mapping unless you implement the slightly more complex
> environmental log page. Which isn't a big deal, except out of the
> hundred or so SCSI devices I have here there isn't a single one that
> supports it it. So in practice this interface would probably only exist
> for the purpose of the libata SATL.
> 
> The other reason the libata approach is slightly less attractive is that
> we need all the same SMART parsing for USB as well. So while it is
> cleaner to hide everything ATA in libata, the reality of USB-ATA bridges
> gets in the way. That is why I previously suggested having a libsmart or
> similar with those common bits.
> 
> Anyway, based on what I've worked on today, I'm not sure that libata is
> necessarily the way to go. Sorry about giving bad advice! We've
> successfully implemented translations for everything else in libata over
> the years without too much trouble. And it's not really that the
> translation is bad. It's more the need to support it for USB as well
> that makes things clunky.
> 
>> I don't understand if that means the SCT read log also works
>> on some SCSI drives, or if it is just a slot-in thing for
>> ATA translation that has no meaning on SCSI drives.
> 
> It's an ATA command.
> 
> One concern I have is wrt. to sensor naming. Maybe my /usr/bin/sensors
> command is too old. But it's pretty hopeless to get sensor readings for

You'll need the command (and libsensors) from the lm-sensors package version
3.5 or later for it to recognize SCSI/ATA drives.

> 100 drives without being able to tell which sensor is for which
> device. Haven't looked into that yet. The links exist in
> /sys/class/hwmon that would allow vendor/model/serial to be queried.
> 

There is a device/ subdirectory which points to that information.
Is that what you are looking for ? "sensors" displays something
like satatemp-scsi-5-0, which matches sd 5:0:0:0:

> Oh, and another issue. While technically legal according to the spec, I
> am not sure it's a good idea to export a sensor per scsi_device. I have
> moved things to scsi_target instead to avoid having bazillions of
> sensors show up. Multi-actuator drives are already shipping.
> 

Not sure I understand what you mean with 'bazillions of sensors' and
'sensor per scsi_device'. Can you elaborate ? I see one sensor per drive,
which is what I would expect.

Thanks,
Guenter

> If I recall correctly, though, I seem to recall that you had some sort
> of multi-LUN external disk box that warranted you working on this in the
> first place. Is that correct? Can you refresh my memory?
>