linux-kernel - Re: [PATCH v2 1/2] hwmon: add ChromeOS EC driver

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Date: Tue, 28 May 2024 10:15:07 +1000
From: Stephen Horvath <s.horvath@...look.com.au>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>,
 Benson Leung <bleung@...omium.org>, Lee Jones <lee@...nel.org>,
 Guenter Roeck <groeck@...omium.org>, linux-kernel@...r.kernel.org,
 linux-hwmon@...r.kernel.org, chrome-platform@...ts.linux.dev,
 Dustin Howett <dustin@...ett.net>,
 Mario Limonciello <mario.limonciello@....com>,
 Moritz Fischer <mdf@...nel.org>
Subject: Re: [PATCH v2 1/2] hwmon: add ChromeOS EC driver

Hi Thomas,

On 28/5/24 05:24, Thomas Weißschuh wrote:
> Hi Stephen,
> 
> 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@...ssschuh.net>
>>> ---
>>>    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@...ssschuh.net>
>>> + */
>>> +
>>> +#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.
> 
> 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.

> And EC_FAN_SPEED_STALLED also sets HWMON_F_FAULT.
> HWMON_F_ALARM doesn't seem right to me.

Fair enough, I thought I copied the behaviour off another driver, but I 
can't find which one, so maybe I just made it up. I do agree with you 
though.

> But if Guenter has a preference, that will do, too.

Of course!

>>
>>> +	*speed = data;
>>> +	return 0;
>>> +}
>>> +
> 
> <snip>
> 
>> But feel free to ignore me if I'm completly wrong about this, since I really
>> don't have much experience with kernel dev.
> 
> Thanks for your feedback!
> 
> Would you mind if I Cc you on further revisions?

Sure, I don't mind at all!
To be honest, I wouldn't mind a Cc on the other Framework related stuff 
too, but I don't mind either way.

Thanks,
Steve