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SubjectRe: [PATCH resend 1/3] hwmon: (lm85) remove freq_map size hardcodes
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
>

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