Re: [PATCH v3 09/10] drivers/hwmon: Add PECI hwmon client drivers

[Guenter Roeck]

On Thu, Apr 12, 2018 at 10:09:51AM -0700, Jae Hyun Yoo wrote:
[ ... ]
> >>>>>>+static int find_core_index(struct peci_cputemp *priv, int channel)
> >>>>>>+{
> >>>>>>+    int core_channel = channel - DEFAULT_CHANNEL_NUMS;
> >>>>>>+    int idx, found = 0;
> >>>>>>+
> >>>>>>+    for (idx = 0; idx < priv->gen_info->core_max; idx++) {
> >>>>>>+        if (priv->core_mask & BIT(idx)) {
> >>>>>>+            if (core_channel == found)
> >>>>>>+                break;
> >>>>>>+
> >>>>>>+            found++;
> >>>>>>+        }
> >>>>>>+    }
> >>>>>>+
> >>>>>>+    return idx;
> >>>>>
> >>>>>What if nothing is found ?
> >>>>>
> >>>>
> >>>>Core temperature group will be registered only when it detects at
> >>>>least one core checked by check_resolved_cores(), so
> >>>>find_core_index() can be called only when priv->core_mask has a
> >>>>non-zero value. The 'nothing is found' case will not happen.
> >>>>
> >>>That doesn't guarantee a match. If what you are saying is correct
> >>>there should always be
> >>>a well defined match of channel -> idx, and the search should be
> >>>unnecessary.
> >>>
> >>
> >>There could be some disabled cores in the resolved core mask bit
> >>sequence also it should remove indexing gap in channel numbering so it
> >>is the reason why this search function is needed. Well defined match of
> >>channel -> idx would not be always satisfied.
> >>
> >Are you saying that each call to the function, with the same parameters,
> >can return a different result ?
> >
> 
> No, the result will be consistent. After reading the priv->core_mask once in
> check_resolved_cores(), the value will not be changed. I'm saying about this
> case, for example if core number 2 is unresolved in total 4 cores, then the
> idx order will be '0, 1, 3' but channel order will be '5, 6, 7' without
> making any indexing gap.
> 

And you yet you claim that this is not well defined ? Or are you concerned
about the amount of memory consumed by providing an array for the mapping ?

Note that an indexing gap is acceptable and, in many cases, preferred.

[ ... ]

> >>>>>>+
> >>>>>>+    dev_dbg(dev, "%s: sensor '%s'\n", dev_name(hwmon_dev),
> >>>>>>priv->name);
> >>>>>>+
> >>>
> >>>Why does this message display the device name twice ?
> >>>
> >>
> >>For an example, dev_name(hwmon_dev) shows 'hwmon5' and priv->name shows
> >>'peci-cputemp0'.
> >>
> >And dev_dbg() shows another device name. So you'll have something like
> >
> >peci-cputemp0: hwmon5: sensor 'peci-cputemp0'
> >
> 
> Practically it shows like
> 
> peci-cputemp 0-30:00: hwmon10: sensor 'peci_cputemp.cpu0'
> 
> where 0-30:00 is assigned by peci core.
> 

And what message would you see for cpu1 ?