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Date:   Wed, 30 Jan 2019 09:25:10 -0800
From:   Guenter Roeck <linux@roeck-us.net>
To:     Jeremy Gebben <jgebben@sweptlaser.com>
Cc:     Jean Delvare <jdelvare@suse.com>, Jonathan Corbet <corbet@lwn.net>,
        linux-hwmon@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH resend 1/3] hwmon: (lm85) remove freq_map size hardcodes
Message-ID: <20190130172510.GB14781@roeck-us.net>
References: <20190129212920.27921-1-jgebben@sweptlaser.com>
 <20190130161447.19946-1-jgebben@sweptlaser.com>
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On Wed, Jan 30, 2019 at 09:14:45AM -0700, Jeremy Gebben wrote:
> 
> Allow support for chips that support more than 8 frequencies.
> The size still must be a power of two.
> 
This is risky. Someone later may not know/remember and 
expand the table without maintaining that restriction.
I would suggest to use map_size instead of map_mask.
While that adds some divide operations, none of those are
in a critical path, and the code would be much more robust.

> Signed-off-by: Jeremy Gebben <jgebben@sweptlaser.com>
> ---
>  drivers/hwmon/lm85.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/hwmon/lm85.c b/drivers/hwmon/lm85.c
> index 0a325878e8f5..48f59667a88c 100644
> --- a/drivers/hwmon/lm85.c
> +++ b/drivers/hwmon/lm85.c
> @@ -198,13 +198,13 @@ static int RANGE_TO_REG(long range)
>  #define RANGE_FROM_REG(val)	lm85_range_map[(val) & 0x0f]
>  
>  /* These are the PWM frequency encodings */
> -static const int lm85_freq_map[8] = { /* 1 Hz */
> +static const int lm85_freq_map[] = { /* 1 Hz */
>  	10, 15, 23, 30, 38, 47, 61, 94
>  };
> -static const int adm1027_freq_map[8] = { /* 1 Hz */
> +
> +static const int adm1027_freq_map[] = { /* 1 Hz */
>  	11, 15, 22, 29, 35, 44, 59, 88
>  };
> -#define FREQ_MAP_LEN	8
>  
>  static int FREQ_TO_REG(const int *map,
>  		       unsigned int map_size, unsigned long freq)
> @@ -212,9 +212,9 @@ static int FREQ_TO_REG(const int *map,
>  	return find_closest(freq, map, map_size);
>  }
>  
> -static int FREQ_FROM_REG(const int *map, u8 reg)
> +static int FREQ_FROM_REG(const int *map, unsigned int map_size, u8 reg)
>  {
> -	return map[reg & 0x07];
> +	return map[reg & (map_size - 1)];

Passing in map_size (calculated as map_mask + 1) just to subtract one
doesn't make sense.

>  }
>  
>  /*
> @@ -296,6 +296,8 @@ struct lm85_data {
>  	struct i2c_client *client;
>  	const struct attribute_group *groups[6];
>  	const int *freq_map;
> +	unsigned int freq_map_mask;
> +
>  	enum chips type;
>  
>  	bool has_vid5;	/* true if VID5 is configured for ADT7463 or ADT7468 */
> @@ -514,7 +516,7 @@ static struct lm85_data *lm85_update_device(struct device *dev)
>  			data->autofan[i].config =
>  			    lm85_read_value(client, LM85_REG_AFAN_CONFIG(i));
>  			val = lm85_read_value(client, LM85_REG_AFAN_RANGE(i));
> -			data->pwm_freq[i] = val & 0x07;
> +			data->pwm_freq[i] = val & data->freq_map_mask;
>  			data->zone[i].range = val >> 4;
>  			data->autofan[i].min_pwm =
>  			    lm85_read_value(client, LM85_REG_AFAN_MINPWM(i));
> @@ -791,7 +793,8 @@ static ssize_t show_pwm_freq(struct device *dev,
>  	if (IS_ADT7468_HFPWM(data))
>  		freq = 22500;
>  	else
> -		freq = FREQ_FROM_REG(data->freq_map, data->pwm_freq[nr]);
> +		freq = FREQ_FROM_REG(data->freq_map, data->freq_map_mask + 1,
> +				     data->pwm_freq[nr]);
>  
>  	return sprintf(buf, "%d\n", freq);
>  }
> @@ -820,7 +823,7 @@ static ssize_t set_pwm_freq(struct device *dev,
>  		lm85_write_value(client, ADT7468_REG_CFG5, data->cfg5);
>  	} else {					/* Low freq. mode */
>  		data->pwm_freq[nr] = FREQ_TO_REG(data->freq_map,
> -						 FREQ_MAP_LEN, val);
> +						 data->freq_map_mask + 1, val);
>  		lm85_write_value(client, LM85_REG_AFAN_RANGE(nr),
>  				 (data->zone[nr].range << 4)
>  				 | data->pwm_freq[nr]);
> @@ -1196,7 +1199,7 @@ static ssize_t set_temp_auto_temp_min(struct device *dev,
>  		TEMP_FROM_REG(data->zone[nr].limit));
>  	lm85_write_value(client, LM85_REG_AFAN_RANGE(nr),
>  		((data->zone[nr].range & 0x0f) << 4)
> -		| (data->pwm_freq[nr] & 0x07));
> +		| data->pwm_freq[nr]);
>  
>  	mutex_unlock(&data->update_lock);
>  	return count;
> @@ -1232,7 +1235,7 @@ static ssize_t set_temp_auto_temp_max(struct device *dev,
>  		val - min);
>  	lm85_write_value(client, LM85_REG_AFAN_RANGE(nr),
>  		((data->zone[nr].range & 0x0f) << 4)
> -		| (data->pwm_freq[nr] & 0x07));
> +		| data->pwm_freq[nr]);
>  	mutex_unlock(&data->update_lock);
>  	return count;
>  }
> @@ -1569,9 +1572,11 @@ static int lm85_probe(struct i2c_client *client, const struct i2c_device_id *id)
>  	case emc6d103:
>  	case emc6d103s:
>  		data->freq_map = adm1027_freq_map;
> +		data->freq_map_mask = ARRAY_SIZE(adm1027_freq_map) - 1;
>  		break;
>  	default:
>  		data->freq_map = lm85_freq_map;
> +		data->freq_map_mask = ARRAY_SIZE(lm85_freq_map) - 1;
>  	}

You'd have to make sure that freq_map_mask is indeed a mask, ie that
ARRAY_SIZE() is a power of two. I would suggest to use freq_map_size
instead.

>  
>  	/* Set the VRM version */
> -- 
> 2.17.1
>