Date:   Mon, 16 Dec 2019 19:57:31 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     linux-hwmon@...r.kernel.org, Jean Delvare <jdelvare@...e.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [PATCH 0/1] Summary: hwmon driver for temperature sensors on SATA
 drives

On 12/16/19 6:35 PM, Martin K. Petersen wrote:
> 
> Guenter,
> 
>> If and when drives are detected which report bad information, such
>> drives can be added to a blacklist without impact on the core SCSI or
>> ATA code. Until that happens, not loading the driver solves the
>> problem on any affected system.
> 
> My only concern with that is that we'll have blacklisting several
> places. We already have ATA and SCSI blacklists. If we now add a third
> place, that's going to be a maintenance nightmare.
> 
> More on that below.
> 
>>> My concerns are wrt. identifying whether SMART data is available for
>>> USB/UAS. I am not too worried about ATA and "real" SCSI (ignoring RAID
>>> controllers that hide the real drives in various ways).
> 
> OK, so I spent my weekend tinkering with 15+ years of accumulated USB
> devices. And my conclusion is that no, we can't in any sensible manner,
> support USB storage monitoring in the kernel. There is no heuristic that
> I can find that identifies that "this is a hard drive or an SSD and
> attempting one of the various SMART methods may be safe". As opposed to
> "this is a USB key that's likely to lock up if you try". And that's
> ignoring the drives with USB-ATA bridges that I managed to wedge in my
> attempt at sending down commands.
> 
> Even smartmontools is failing to work on a huge part of my vintage
> collection.  Thanks to a wide variety of bridges with random, custom
> interfaces.
> 
> So my stance on all this is that I'm fine with your general approach for
> ATA. I will post a patch adding the required bits for SCSI. And if a
> device does not implement either of the two standard methods, people
> should use smartmontools.
> 
> Wrt. name, since I've added SCSI support, satatemp is a bit of a
> misnomer. drivetemp, maybe? No particular preference.
> 
Agreed, if we extend this to SCSI, satatemp is less than perfect.
drivetemp ? disktemp ? I am open to suggestions, with maybe a small
personal preference for disktemp out of those two.

>> The one USB/UAS connected SATA drive I have (a WD passport) reports
>> itself as "WD      ", not as "ATA     ". I would expect other drives
>> to do the same.
> 
> Yes. Most vendors are too fond of their brand names to put "ATA" in
> there. So my suggestion is to relax the heuristic to trigger on the ATA
> Information VPD page only and ignore the name.
> 

Fine with me. I wanted to be as restrictive as possible.

> Also, there are some devices that will lock up the way you access that
> VPD page. So a tweak is also required there.
> 
Do you have details ? Do I need to add a call to scsi_device_supports_vpd(),
maybe ?

> To avoid the multiple blacklists and heuristic collections my suggestion
> is that I introduce a helper function in SCSI (based on what I did in
> the disk driver) that can be called to identify whether something is an
> ATA device. And then the hwmon driver can call that and we can keep the
> heuristics in one place.
> 
> If a device turns out to be problematic wrt. getting the ATA VPD for the
> purpose of SMART, for instance, it will also need to be blacklisted for
> other reasons in SCSI. So I would really like to keep the heuristics in
> one place.
> 
Fine with me. My only concern is that I don't want the driver to disappear
into nowhere-land (again).

Thanks,
Guenter

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