[PATCH] NVMe: Log Sense Temperature doesn't handle negative values

[Jeffrey Lien]

Attached an updated patch with change Jon recommended below.   


-----Original Message-----
From: Linux-nvme [mailto:linux-nvme-bounces at lists.infradead.org] On Behalf Of Jeffrey Lien
Sent: Monday, October 12, 2015 3:25 PM
To: Jon Derrick <jonathan.derrick at intel.com>; Keith Busch <keith.busch at intel.com>
Cc: axboe at fb.com; David Darrington <david.darrington at hgst.com>; linux-nvme at lists.infradead.org
Subject: RE: [PATCH] NVMe: Log Sense Temperature doesn't handle negative values



-----Original Message-----
From: Jon Derrick [mailto:jonathan.derrick at intel.com]
Sent: Friday, October 9, 2015 3:41 PM
To: Keith Busch <keith.busch at intel.com>
Cc: Jeffrey Lien <Jeff.Lien at hgst.com>; axboe at fb.com; David Darrington <david.darrington at hgst.com>; linux-nvme at lists.infradead.org
Subject: Re: [PATCH] NVMe: Log Sense Temperature doesn't handle negative values

On Fri, Oct 09, 2015 at 02:15:33PM -0600, Jon Derrick wrote:
>> > >To meet the SCSI Command Spec (T10 SPC-4 r37), the log sense temperature cannot
>> > >be negative.   From the spec:
>> > >
>> > >The TEMPERATURE field indicates the temperature of the SCSI target 
>> > >device in degrees Celsius at the time the LOG SENSE command is 
>> > >performed. Temperatures equal to or less than zero degrees Celsius 
>> > >shall cause the TEMPERATURE field to be set to zero. If the device 
>> > >server is unable to detect a valid temperature because of a sensor 
>> > >failure or other condition, then the TEMPERATURE field shall be 
>> > >set to FFh. The temperature should be reported with an accuracy of 
>> > >plus or minus three Celsius degrees while the SCSI target device is operating at a steady state within its environmental limits.
>> > >
>> > >With the current code, a value of -2 C will be shown as 254 C 
>> > >since it was not written to handle negative vales.  This same 
>> > >issue also exists in nvme_trans_log_info_exceptions.
>> > 
>> > [snip]
>> > 
>> > >@@ -1097,7 +1101,7 @@ static int nvme_trans_log_temperature(struct nvme_ns *ns, struct sg_io_hdr *hdr,
>> > > 	dma_addr_t dma_addr;
>> > > 	void *mem;
>> > > 	u32 feature_resp;
>> > >-	u8 temp_c_cur, temp_c_thresh;
>> > >+	s8 temp_c_cur, temp_c_thresh;
>> > > 	u16 temp_k;
>> > > 	log_response = kzalloc(LOG_TEMP_PAGE_LENGTH, GFP_KERNEL); @@
>> > >-1129,6 +1133,10 @@ static int nvme_trans_log_temperature(struct nvme_ns *ns, struct sg_io_hdr *hdr,
>> > > 		temp_k = (smart_log->temperature[1] << 8) +
>> > > 				(smart_log->temperature[0]);
>> > > 		temp_c_cur = temp_k - KELVIN_TEMP_FACTOR;
>> > >+		/* if temp_c_cur is negative,          */
>> > >+		/* set to 0 to meet Scsi Command Spec  */
>> > >+		if (temp_c_cur < 0)
>> > >+			temp_c_cur = 0;
>> > 
>> > Interesting, < 0C is colder than I might have expected. What if 
>> > they can get hotter than expected, like 128C? I don't think we want 
>> > to report that as 0.
>> >
>> 
>> It's unfortunate the spec is written that way. Aerospace silicon is 
>> often rated for -55/-40C to +125C junction temp +/- a few %. Thats a 
>> big negative range missing if it has to be 0. I would imagine over 
>> 128C is not meaningful so we would want to report that as 128C
>> 

>Thinking about it again, I would much rather see the u8 being used so we get the full range.

>something like this should do:
>temp_c_cur = temp_k < KELVIN_TEMP_FACTOR ? 0 : temp_k - 
>KELVIN_TEMP_FACTOR;

I like that solution; simple and straight forward.   Want me to resubmit the patch with Jon's suggested change?
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