Weird interaction between thermal and cpufreq drivers

Hello linux-pm,

I'm seeing a weird bug, where the thermal driver(*) returns bogus temperatures once I lower the CPU frequency.

(*) drivers/thermal/tango_thermal.c

The setup: I'm using next-20160428
(Is it a good idea to test on linux-next?
Are there bugs lurking there that get sorted out later?)

I have a script which prints /sys/class/thermal/thermal_zone0/temp every second.

When the CPU is running at nominal speed, these values seem correct. ("seem" because I don't have the HW to calibrate the thermometer.)

But once I lower the frequency of the CPU(*), the script starts printing bogus values like 29000 (my driver's minimum) and very high temps like 100000 or even 137000!

(*) echo 135000 > /sys/devices/system/cpu/cpufreq/scaling_max_freq I'm using the performance governor, so everything should be manual, if I understand correctly.

I looked at timing issues in my driver. I do have an obvious usleep_range(10, 20); in my code. IIUC, this primitive will use the underlying Cortex A9 twd block, which does introduce errors on frequency changes, so I switched it to udelay(100); This one should only use the platform tick counter, which ticks at a constant speed. But I still have the issues.

Any idea what could be going wrong?

I guess I can test on v4.6-rc5

Regards.

Egg on my face...

cpufreq was a red herring. I simply failed to initialize TEMPSI_CFG. (And the hardware playfully sets it to an arbitrary value at reset.) Patch incoming.

Regards.

From: Marc Gonzalez <[email protected]>

TEMPSI_CFG is not equal to 0 at reset. It must be initialized.

---
 drivers/thermal/tango_thermal.c | 1 +
 1 file changed, 1 insertion(+)

index 22f9b1e92db1..70e0d9f406e9 100644
@@ -80,6 +80,7 @@ static int tango_thermal_probe(struct platform_device *pdev)
 		return PTR_ERR(priv->base);
 
 	priv->thresh_idx = IDX_MIN;
+	writel(0, priv->base + TEMPSI_CFG);
 	writel(CMD_ON, priv->base + TEMPSI_CMD);
 
 	tzdev = devm_thermal_zone_of_sensor_register(&pdev->dev, 0, priv, &ops);

2.8.1