Re: [PATCH v4] power: supply: core: Use library interpolation

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Hi Linus,

On 2021/11/17 7:02, Linus Walleij wrote:
> The power supply core appears to contain two open coded
> linear interpolations. Use the kernel fixpoint arithmetic
> interpolation library function instead.
> 
> Cc: Chunyan Zhang <chunyan.zhang@unisoc.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

LGTM. Thanks :)
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

> ---
> ChangeLog v3->v4:
> - Fix the code to really provide the same x index for both
>    datapoints at the end of the table. Thanks again Baolin!
> ChangeLog v2->v3:
> - Actually implement the code as I say. Missed one occurence.
> ChangeLog v1->v2:
> - Break the table loop at table_len - 1 so we don't index
>    past the end of the table. (Thanks Baolin!)
> 
> Chunyan: The sc27xx fuel gauge seems to be the only driver
> using this, so it'd be great if you could test this to make
> sure it works as intended.
> ---
>   drivers/power/supply/power_supply_core.c | 61 ++++++++++++------------
>   1 file changed, 31 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/power/supply/power_supply_core.c b/drivers/power/supply/power_supply_core.c
> index fc12a4f407f4..2907b84ceea9 100644
> --- a/drivers/power/supply/power_supply_core.c
> +++ b/drivers/power/supply/power_supply_core.c
> @@ -21,6 +21,7 @@
>   #include <linux/power_supply.h>
>   #include <linux/property.h>
>   #include <linux/thermal.h>
> +#include <linux/fixp-arith.h>
>   #include "power_supply.h"
>   
>   /* exported for the APM Power driver, APM emulation */
> @@ -783,26 +784,25 @@ EXPORT_SYMBOL_GPL(power_supply_put_battery_info);
>   int power_supply_temp2resist_simple(struct power_supply_resistance_temp_table *table,
>   				    int table_len, int temp)
>   {
> -	int i, resist;
> +	int i, high, low;
>   
> -	for (i = 0; i < table_len; i++)
> +	/* Break loop at table_len - 1 because that is the highest index */
> +	for (i = 0; i < table_len - 1; i++)
>   		if (temp > table[i].temp)
>   			break;
>   
> -	if (i > 0 && i < table_len) {
> -		int tmp;
> -
> -		tmp = (table[i - 1].resistance - table[i].resistance) *
> -			(temp - table[i].temp);
> -		tmp /= table[i - 1].temp - table[i].temp;
> -		resist = tmp + table[i].resistance;
> -	} else if (i == 0) {
> -		resist = table[0].resistance;
> -	} else {
> -		resist = table[table_len - 1].resistance;
> -	}
> -
> -	return resist;
> +	/* The library function will deal with high == low */
> +	if ((i == 0) || (i == (table_len - 1)))
> +		high = i;
> +	else
> +		high = i - 1;
> +	low = i;
> +
> +	return fixp_linear_interpolate(table[low].temp,
> +				       table[low].resistance,
> +				       table[high].temp,
> +				       table[high].resistance,
> +				       temp);
>   }
>   EXPORT_SYMBOL_GPL(power_supply_temp2resist_simple);
>   
> @@ -821,24 +821,25 @@ EXPORT_SYMBOL_GPL(power_supply_temp2resist_simple);
>   int power_supply_ocv2cap_simple(struct power_supply_battery_ocv_table *table,
>   				int table_len, int ocv)
>   {
> -	int i, cap, tmp;
> +	int i, high, low;
>   
> -	for (i = 0; i < table_len; i++)
> +	/* Break loop at table_len - 1 because that is the highest index */
> +	for (i = 0; i < table_len - 1; i++)
>   		if (ocv > table[i].ocv)
>   			break;
>   
> -	if (i > 0 && i < table_len) {
> -		tmp = (table[i - 1].capacity - table[i].capacity) *
> -			(ocv - table[i].ocv);
> -		tmp /= table[i - 1].ocv - table[i].ocv;
> -		cap = tmp + table[i].capacity;
> -	} else if (i == 0) {
> -		cap = table[0].capacity;
> -	} else {
> -		cap = table[table_len - 1].capacity;
> -	}
> -
> -	return cap;
> +	/* The library function will deal with high == low */
> +	if ((i == 0) || (i == (table_len - 1)))
> +		high = i - 1;
> +	else
> +		high = i; /* i.e. i == 0 */
> +	low = i;
> +
> +	return fixp_linear_interpolate(table[low].ocv,
> +				       table[low].capacity,
> +				       table[high].ocv,
> +				       table[high].capacity,
> +				       ocv);
>   }
>   EXPORT_SYMBOL_GPL(power_supply_ocv2cap_simple);
>   
>