Re: [PATCH v2 1/2] hwmon: add ChromeOS EC driver
From: Guenter Roeck
Date: Tue May 28 2024 - 19:30:10 EST
On 5/28/24 09:15, Thomas Weißschuh wrote:
On 2024-05-28 08:50:49+0000, Guenter Roeck wrote:
On 5/27/24 17:15, Stephen Horvath wrote:
On 28/5/24 05:24, Thomas Weißschuh wrote:
On 2024-05-25 09:13:09+0000, Stephen Horvath wrote:
I was the one to implement fan monitoring/control into Dustin's driver, and
just had a quick comment for your driver:
On 8/5/24 02:29, Thomas Weißschuh wrote:
The ChromeOS Embedded Controller exposes fan speed and temperature
readings.
Expose this data through the hwmon subsystem.
The driver is designed to be probed via the cros_ec mfd device.
Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
---
Documentation/hwmon/cros_ec_hwmon.rst | 26 ++++
Documentation/hwmon/index.rst | 1 +
MAINTAINERS | 8 +
drivers/hwmon/Kconfig | 11 ++
drivers/hwmon/Makefile | 1 +
drivers/hwmon/cros_ec_hwmon.c | 269 ++++++++++++++++++++++++++++++++++
6 files changed, 316 insertions(+)
<snip>
diff --git a/drivers/hwmon/cros_ec_hwmon.c b/drivers/hwmon/cros_ec_hwmon.c
new file mode 100644
index 000000000000..d59d39df2ac4
--- /dev/null
+++ b/drivers/hwmon/cros_ec_hwmon.c
@@ -0,0 +1,269 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * ChromesOS EC driver for hwmon
+ *
+ * Copyright (C) 2024 Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
+ */
+
+#include <linux/device.h>
+#include <linux/hwmon.h>
+#include <linux/kernel.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/platform_data/cros_ec_commands.h>
+#include <linux/platform_data/cros_ec_proto.h>
+#include <linux/units.h>
+
+#define DRV_NAME "cros-ec-hwmon"
+
+struct cros_ec_hwmon_priv {
+ struct cros_ec_device *cros_ec;
+ u8 thermal_version;
+ const char *temp_sensor_names[EC_TEMP_SENSOR_ENTRIES + EC_TEMP_SENSOR_B_ENTRIES];
+};
+
+static int cros_ec_hwmon_read_fan_speed(struct cros_ec_device *cros_ec, u8 index, u16 *speed)
+{
+ u16 data;
+ int ret;
+
+ ret = cros_ec->cmd_readmem(cros_ec, EC_MEMMAP_FAN + index * 2, 2, &data);
+ if (ret < 0)
+ return ret;
+
+ data = le16_to_cpu(data);
+
+ if (data == EC_FAN_SPEED_NOT_PRESENT)
+ return -ENODEV;
+
Don't forget it can also return `EC_FAN_SPEED_STALLED`.
Thanks for the hint. I'll need to think about how to handle this better.
Like Guenter, I also don't like returning `-ENODEV`, but I don't have a
problem with checking for `EC_FAN_SPEED_NOT_PRESENT` in case it was removed
since init or something.
That won't happen. Chromebooks are not servers, where one might be able to
replace a fan tray while the system is running.
In one of my testruns this actually happened.
When running on battery, one specific of the CPU sensors sporadically
returned EC_FAN_SPEED_NOT_PRESENT.
What Chromebook was that ? I can't see the code path in the EC source
that would get me there.
Ok.
My approach was to return the speed as `0`, since the fan probably isn't
spinning, but set HWMON_F_FAULT for `EC_FAN_SPEED_NOT_PRESENT` and
HWMON_F_ALARM for `EC_FAN_SPEED_STALLED`.
No idea if this is correct though.
I'm not a fan of returning a speed of 0 in case of errors.
Rather -EIO which can't be mistaken.
Maybe -EIO for both EC_FAN_SPEED_NOT_PRESENT (which should never happen)
and also for EC_FAN_SPEED_STALLED.
Yeah, that's pretty reasonable.
-EIO is an i/o error. I have trouble reconciling that with
EC_FAN_SPEED_NOT_PRESENT or EC_FAN_SPEED_STALLED.
Looking into the EC source code [1], I see:
EC_FAN_SPEED_NOT_PRESENT means that the fan is not present.
That should return -ENODEV in the above code, but only for
the purpose of making the attribute invisible.
EC_FAN_SPEED_STALLED means exactly that, i.e., that the fan
is present but not turning. The EC code does not expect that
to happen and generates a thermal event in case it does.
Given that, it does make sense to set the fault flag.
The actual fan speed value should then be reported as 0 or
possibly -ENODATA. It should _not_ generate any other error
because that would trip up the "sensors" command for no
good reason.
Ack.
Currently I have the following logic (for both fans and temp):
if NOT_PRESENT during probing:
make the attribute invisible.
if any error during runtime (including NOT_PRESENT):
return -ENODATA and a FAULT
This should also handle the sporadic NOT_PRESENT failures.
What do you think?
Is there any other feedback to this revision or should I send the next?
No, except I'd really like to know which Chromebook randomly generates
a EC_FAN_SPEED_NOT_PRESENT response because that really looks like a bug.
Also, can you reproduce the problem with the ectool command ?
Thanks,
Guenter