Re: [PATCH v2 1/2] hwmon: (amd_energy) Use unified function to read energy data

[Jean Delvare <jdelvare@suse.de>]

Hi Guenter,

On Fri,  9 Apr 2021 10:48:51 -0700, Guenter Roeck wrote:
> The driver implements two separate functions to read and update
> energy values. One function is called periodically and updates
> cached enery information to avoid loss of data, the other reads
> energy data on demand to report it to userspace. The second
> function reads current energy data, adds the difference to the
> data previously obtained by the first function, and then discards
> the updated data.
> 
> Simplify the code and always call the first function, then report
> the energy data obtained by this function to userspace.

I like the idea.

> Cc: Naveen Krishna Chatradhi <nchatrad@amd.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> v2: Added patch, simplification
> 
>  drivers/hwmon/amd_energy.c | 31 ++++++-------------------------
>  1 file changed, 6 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/hwmon/amd_energy.c b/drivers/hwmon/amd_energy.c
> index a86cc8d6d93d..93bad64039f1 100644
> --- a/drivers/hwmon/amd_energy.c
> +++ b/drivers/hwmon/amd_energy.c
> @@ -118,35 +118,12 @@ static void read_accumulate(struct amd_energy_data *data)
>  	data->core_id++;
>  }
>  
> -static void amd_add_delta(struct amd_energy_data *data, int ch,
> -			  int cpu, long *val, u32 reg)
> -{
> -	struct sensor_accumulator *accum;
> -	u64 input;
> -
> -	mutex_lock(&data->lock);
> -	rdmsrl_safe_on_cpu(cpu, reg, &input);
> -	input &= AMD_ENERGY_MASK;
> -
> -	accum = &data->accums[ch];
> -	if (input >= accum->prev_value)
> -		input += accum->energy_ctr -
> -				accum->prev_value;
> -	else
> -		input += UINT_MAX - accum->prev_value +
> -				accum->energy_ctr;
> -
> -	/* Energy consumed = (1/(2^ESU) * RAW * 1000000UL) μJoules */
> -	*val = div64_ul(input * 1000000UL, BIT(data->energy_units));
> -
> -	mutex_unlock(&data->lock);
> -}
> -
>  static int amd_energy_read(struct device *dev,
>  			   enum hwmon_sensor_types type,
>  			   u32 attr, int channel, long *val)
>  {
>  	struct amd_energy_data *data = dev_get_drvdata(dev);
> +	struct sensor_accumulator *accum;
>  	u32 reg;
>  	int cpu;
>  
> @@ -162,7 +139,11 @@ static int amd_energy_read(struct device *dev,
>  
>  		reg = ENERGY_CORE_MSR;
>  	}
> -	amd_add_delta(data, channel, cpu, val, reg);
> +
> +	accumulate_delta(data, channel, cpu, reg);
> +	accum = &data->accums[channel];
> +
> +	*val = div64_ul(accum->energy_ctr * 1000000UL, BIT(data->energy_units));

Is it considered safe to read accum->energy_ctr while not holding
data->lock?

>  
>  	return 0;
>  }

If the answer to the question above is "yes" then:

Reviewed-by: Jean Delvare <jdelvare@suse.de>

-- 
Jean Delvare
SUSE L3 Support