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Sender: Guenter Roeck <groeck7@gmail.com>
Date: Tue, 16 Apr 2024 06:30:59 -0700
From: Guenter Roeck <linux@roeck-us.net>
To: Maximilian Luz <luzmaximilian@gmail.com>
Cc: Jean Delvare <jdelvare@suse.com>,
	Ilpo =?iso-8859-1?Q?J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>,
	Hans de Goede <hdegoede@redhat.com>,
	Ivor Wanders <ivor@iwanders.net>, linux-kernel@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, linux-hwmon@vger.kernel.org
Subject: Re: [PATCH 2/3] hwmon: surface_temp: Add support for sensor names
Message-ID: <43908511-198f-42ee-af21-dad79bdf799a@roeck-us.net>
References: <20240330112409.3402943-1-luzmaximilian@gmail.com>
 <20240330112409.3402943-3-luzmaximilian@gmail.com>
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On Sat, Mar 30, 2024 at 12:24:01PM +0100, Maximilian Luz wrote:
> From: Ivor Wanders <ivor@iwanders.net>
> 
> The thermal subsystem of the Surface Aggregator Module allows us to
> query the names of the respective thermal sensors. Forward those to
> userspace.
> 
> Signed-off-by: Ivor Wanders <ivor@iwanders.net>
> Co-developed-by: Maximilian Luz <luzmaximilian@gmail.com>
> Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
> Reviewed-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/hwmon/surface_temp.c | 112 +++++++++++++++++++++++++++++------
>  1 file changed, 95 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/hwmon/surface_temp.c b/drivers/hwmon/surface_temp.c
> index 48c3e826713f6..7a2e1f638336c 100644
> --- a/drivers/hwmon/surface_temp.c
> +++ b/drivers/hwmon/surface_temp.c
> @@ -17,6 +17,27 @@
>  
>  /* -- SAM interface. -------------------------------------------------------- */
>  
> +/*
> + * Available sensors are indicated by a 16-bit bitfield, where a 1 marks the
> + * presence of a sensor. So we have at most 16 possible sensors/channels.
> + */
> +#define SSAM_TMP_SENSOR_MAX_COUNT 16

#define<space>DEFINITION<tab>value

> +
> +/*
> + * All names observed so far are 6 characters long, but there's only
> + * zeros after the name, so perhaps they can be longer. This number reflects
> + * the maximum zero-padded space observed in the returned buffer.
> + */
> +#define SSAM_TMP_SENSOR_NAME_LENGTH 18
> +
> +struct ssam_tmp_get_name_rsp {
> +	__le16 unknown1;
> +	char unknown2;
> +	char name[SSAM_TMP_SENSOR_NAME_LENGTH];
> +} __packed;
> +
> +static_assert(sizeof(struct ssam_tmp_get_name_rsp) == 21);
> +
>  SSAM_DEFINE_SYNC_REQUEST_CL_R(__ssam_tmp_get_available_sensors, __le16, {
>  	.target_category = SSAM_SSH_TC_TMP,
>  	.command_id      = 0x04,
> @@ -27,6 +48,11 @@ SSAM_DEFINE_SYNC_REQUEST_MD_R(__ssam_tmp_get_temperature, __le16, {
>  	.command_id      = 0x01,
>  });
>  
> +SSAM_DEFINE_SYNC_REQUEST_MD_R(__ssam_tmp_get_name, struct ssam_tmp_get_name_rsp, {
> +	.target_category = SSAM_SSH_TC_TMP,
> +	.command_id      = 0x0e,
> +});
> +
>  static int ssam_tmp_get_available_sensors(struct ssam_device *sdev, s16 *sensors)
>  {
>  	__le16 sensors_le;
> @@ -54,12 +80,37 @@ static int ssam_tmp_get_temperature(struct ssam_device *sdev, u8 iid, long *temp
>  	return 0;
>  }
>  
> +static int ssam_tmp_get_name(struct ssam_device *sdev, u8 iid, char *buf, size_t buf_len)
> +{
> +	struct ssam_tmp_get_name_rsp name_rsp;
> +	int status;
> +
> +	status =  __ssam_tmp_get_name(sdev->ctrl, sdev->uid.target, iid, &name_rsp);
> +	if (status)
> +		return status;
> +
> +	/*
> +	 * This should not fail unless the name in the returned struct is not
> +	 * null-terminated or someone changed something in the struct
> +	 * definitions above, since our buffer and struct have the same
> +	 * capacity by design. So if this fails blow this up with a warning.
> +	 * Since the more likely cause is that the returned string isn't
> +	 * null-terminated, we might have received garbage (as opposed to just
> +	 * an incomplete string), so also fail the function.
> +	 */
> +	status = strscpy(buf, name_rsp.name, buf_len);
> +	WARN_ON(status < 0);

Not acceptable. From include/asm-generic/bug.h:

 * Do not use these macros when checking for invalid external inputs
 * (e.g. invalid system call arguments, or invalid data coming from
 * network/devices), and on transient conditions like ENOMEM or EAGAIN.
 * These macros should be used for recoverable kernel issues only.

> +
> +	return status < 0 ? status : 0;
> +}
> +
>  
>  /* -- Driver.---------------------------------------------------------------- */
>  
>  struct ssam_temp {
>  	struct ssam_device *sdev;
>  	s16 sensors;
> +	char names[SSAM_TMP_SENSOR_MAX_COUNT][SSAM_TMP_SENSOR_NAME_LENGTH];
>  };
>  
>  static umode_t ssam_temp_hwmon_is_visible(const void *data,
> @@ -83,33 +134,47 @@ static int ssam_temp_hwmon_read(struct device *dev,
>  	return ssam_tmp_get_temperature(ssam_temp->sdev, channel + 1, value);
>  }
>  
> +static int ssam_temp_hwmon_read_string(struct device *dev,
> +				       enum hwmon_sensor_types type,
> +				       u32 attr, int channel, const char **str)
> +{
> +	const struct ssam_temp *ssam_temp = dev_get_drvdata(dev);
> +
> +	*str = ssam_temp->names[channel];
> +	return 0;
> +}
> +
>  static const struct hwmon_channel_info * const ssam_temp_hwmon_info[] = {
>  	HWMON_CHANNEL_INFO(chip,
>  			   HWMON_C_REGISTER_TZ),
> -	/* We have at most 16 thermal sensor channels. */
> +	/*
> +	 * We have at most SSAM_TMP_SENSOR_MAX_COUNT = 16 thermal sensor
> +	 * channels.
> +	 */

Pointless comment. Already explained above, and perfect example showing
why it has no value separating this and the previous patch.

>  	HWMON_CHANNEL_INFO(temp,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT,
> -			   HWMON_T_INPUT),
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL),

Another example. Why have me review the previous patch
just to change the code here ?

[ ... ]

> +	/* Retrieve the name for each available sensor. */
> +	for (channel = 0; channel < SSAM_TMP_SENSOR_MAX_COUNT; channel++) {
> +		if (!(sensors & BIT(channel)))
> +			continue;
> +
> +		status = ssam_tmp_get_name(sdev, channel + 1,
> +					   ssam_temp->names[channel],
> +					   SSAM_TMP_SENSOR_NAME_LENGTH);
> +		if (status)
> +			return status;

Your call to fail probe in this case just because it can not find
a sensor name. I personally find that quite aggressive.

Guenter