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

[keith.busch@intel.com (Keith Busch)]

On Thu, 8 Oct 2015, Jeffrey Lien wrote:
> From 4f8b0146b5d310b944cb99b5a68deed08ed89b6b Mon Sep 17 00:00:00 2001
> From: Jeff Lien <jlien at ddtest-jeff.hgst.com>
> Date: Wed, 7 Oct 2015 14:25:07 -0500
> Subject: [PATCH] NVMe: Log Sense Temperature doesn't handle negative values
>  properly.
> 
> 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.