[PATCH 1/3] hwmon: (coretemp) Refresh the temperature on the first read

[Ricardo Neri <ricardo.neri-calderon@linux.intel.com>]

show_temp() reads the status MSR only when the cached temperature is
older than one second. Commit 5c0e64dde80f ("hwmon: (coretemp) Remove
obsolete temp_data->valid") dropped the tdata->valid check that used to
force the very first read, leaving that comparison as the only trigger.

A never-updated temp_data carries a zero timestamp, which does not look
stale on 32-bit kernels: jiffies starts 300 seconds short of wrapping,
so the comparison stays false until jiffies wraps and passes HZ. For the
first 301 seconds of uptime temp%d_input reports the zero left by the
allocator rather than the CPU temperature. 64-bit kernels are
unaffected: jiffies starts at a positive value there and does not wrap.

Backdate the timestamp when the temperature data is allocated. One jiffy
older than the caching interval is stale under either word size, and the
first refresh overwrites it.

Fixes: 5c0e64dde80f ("hwmon: (coretemp) Remove obsolete temp_data->valid")
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
 drivers/hwmon/coretemp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index 5095eb057680..ace51e08e72d 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -511,6 +511,11 @@ init_temp_data(struct platform_data *pdata, unsigned int cpu, int pkg_flag)
 	tdata->cpu = cpu;
 	tdata->cpu_core_id = topology_core_id(cpu);
 	tdata->attr_size = MAX_CORE_ATTRS;
+	/*
+	 * A zero timestamp does not look stale on 32-bit, where jiffies
+	 * starts just short of wrapping. Backdate it instead.
+	 */
+	tdata->last_updated = jiffies - HZ - 1;
 	mutex_init(&tdata->update_lock);
 	return tdata;
 }

-- 
2.43.0