linux-kernel - Re: [PATCH v3 2/3] hwmon: add ChromeOS EC driver

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Message-ID: <ZlWIEUv6kAG2ZO2x@google.com>
Date: Tue, 28 May 2024 07:30:25 +0000
From: Tzung-Bi Shih <tzungbi@...nel.org>
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>,
	Stephen Horvath <s.horvath@...look.com.au>,
	Rajas Paranjpe <paranjperajas@...il.com>
Subject: Re: [PATCH v3 2/3] hwmon: add ChromeOS EC driver

On Tue, May 28, 2024 at 09:09:28AM +0200, Thomas Weißschuh wrote:
> On 2024-05-28 06:39:25+0000, Tzung-Bi Shih wrote:
> > On Mon, May 27, 2024 at 10:58:32PM +0200, Thomas Weißschuh wrote:
> > > +struct cros_ec_hwmon_priv {
> > > +	struct cros_ec_device *cros_ec;
> > > +	const char *temp_sensor_names[EC_TEMP_SENSOR_ENTRIES + EC_TEMP_SENSOR_B_ENTRIES];
> > > +	u8 usable_fans;
> > > +};
> > > +
> > > +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);
> > > +	*speed = data;
> > > +
> > > +	if (data == EC_FAN_SPEED_NOT_PRESENT || data == EC_FAN_SPEED_STALLED)
> > > +		return -EIO;
> > 
> > `data` could be eliminated; use `*speed` instead.
> 
> Then the le16 value would need to be written directly to the out
> parameter. The current usage relies on *speed (sometimes) being set even
> if ret != 0.
> 
> (See next response block)
> 
> > 
> > > +static int cros_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
> > > +			      u32 attr, int channel, long *val)
> > > +{
> > [...]
> > > +	u16 speed = 0;
> > > +	u8 temp = 0;
> > 
> > They don't need to initialize.
> 
> They need to.
> 
> The logic
> 
> if (ret == -EIO && speed == EC_FAN_SPEED_STALLED)
> 	ret = 0;
> 
> relies on -EIO and a write to speed from cros_ec_hwmon_read_fan_speed().
> 
> But if cros_ec_cmd_readmem() already returns -EIO, then speed would be
> uninitialized.

I see.