Weird interaction between thermal and cpufreq drivers

Weird interaction between thermal and cpufreq drivers

[Mason]

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.

Re: Weird interaction between thermal and cpufreq drivers

[Mason]

On 28/04/2016 17:24, Mason wrote:

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

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.

[PATCH] thermal: tango: initialize TEMPSI_CFG

[Mason]

From: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>

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

Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
---
 drivers/thermal/tango_thermal.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/thermal/tango_thermal.c b/drivers/thermal/tango_thermal.c
index 22f9b1e92db1..70e0d9f406e9 100644
--- a/drivers/thermal/tango_thermal.c
+++ b/drivers/thermal/tango_thermal.c
@@ -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