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Date: Tue, 20 Oct 2015 09:58:41 +0200
From: Marc Titinger <mtitinger@...libre.com>
To: Guenter Roeck <linux@...ck-us.net>, jdelvare@...e.com
Cc: lm-sensors@...sensors.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] hwmon: ina2xx: allow for actual measurement bandwidth above
160 Hz
On 20/10/2015 03:32, Guenter Roeck wrote:
> On 10/19/2015 09:21 AM, Marc Titinger wrote:
>> With the current implementation, the driver will prevent a readout at a
>> pace faster than the default conversion time (2ms) times the averaging
>> setting, min AVG being 1:1.
>>
>> Any sysfs "show" read access from the client app faster than 500 Hz
>> will be
>> 'cached' by the driver, but actually since do_update reads all 8
>> registers,
>> the best achievable measurement rate is roughly 8*800 us (for the time
>> spent in i2c-core) i.e. <= 156Hz with Beagle Bone Black.
>>
>> This change set uses a register mask to allow for the readout of a single
>> i2c register at a time. Furthermore, performing subsequent reads on the
>> same register will make use of the ability of the i2c chip to retain the
>> last reg offset, hence use a shorter i2c message (roughly 400us
>> instead of
>> 800us spent in i2c-core.c).
>>
>> The best readout rate for a single measurement is now around 2kHz. And
>> for
>> four measurements around (1/(4*800us) = 312 Hz. Since for any readout
>> rate
>> faster than 160 Hz the interval is set by the i2c transactions
>> completion,
>> the 'last-update' anti-flooding code will not have a limiting effect in
>> practice. Hence I also remove the elapsed time checking in the hwmon
>> driver
>> for ina2xx.
>>
>> To summarize, the patch provides a max bandwidth improvement with hwmon
>> client apps from ~160 Hz to ~320 Hz, and better in single-channel
>> polling mode.
>>
>
Hi Guenter,
> I really dislike that complexity. Maybe we should drop caching entirely
> in this driver ? Maybe even convert it to use regmap ?
I dropped caching completely with this patch. The only (mild!)
complexity added is to keep track of the current register pointer
set in the chip, to issue a shorter i2c message.
Thanks for the hint re. regmap, is there a driver file you recommend I
look into (because the i2c caps were close to in2xx) ?
Many thanks,
Marc.
>
> Guenter
>
>> Signed-off-by: Marc Titinger <mtitinger@...libre.com>
>> ---
>> drivers/hwmon/ina2xx.c | 90
>> +++++++++++++++++++++++++++++++++++++++-----------
>> 1 file changed, 71 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
>> index 4d28150..ce3a2ee 100644
>> --- a/drivers/hwmon/ina2xx.c
>> +++ b/drivers/hwmon/ina2xx.c
>> @@ -48,6 +48,8 @@
>> #define INA2XX_CURRENT 0x04 /* readonly */
>> #define INA2XX_CALIBRATION 0x05
>>
>> +#define BITPOS_TO_MASK(x) (1L << x)
>> +
>> /* INA226 register definitions */
>> #define INA226_MASK_ENABLE 0x06
>> #define INA226_ALERT_LIMIT 0x07
>> @@ -105,9 +107,14 @@ struct ina2xx_data {
>>
>> struct mutex update_lock;
>> bool valid;
>> - unsigned long last_updated;
>> int update_interval; /* in jiffies */
>>
>> + /* Last read register (slave address already set
>> + * reading out from this same register repeatedly will
>> + * be significantly faster!
>> + */
>> + int last_reg;
>> +
>> int kind;
>> const struct attribute_group *groups[INA2XX_MAX_ATTRIBUTE_GROUPS];
>> u16 regs[INA2XX_MAX_REGISTERS];
>> @@ -203,21 +210,63 @@ static int ina2xx_init(struct ina2xx_data *data)
>> return ina2xx_calibrate(data);
>> }
>>
>> -static int ina2xx_do_update(struct device *dev)
>> +/*
>> + * Most I2c chips will allow reading from the current register pointer
>> + * w/o setting the register offset again.
>> + */
>> +static inline s32 __i2c_read_same_word(const struct i2c_client *client)
>> +{
>> + unsigned char msgbuf[2];
>> +
>> + struct i2c_msg msg = {
>> + .addr = client->addr,
>> + .flags = client->flags | I2C_M_RD,
>> + .len = 2,
>> + .buf = msgbuf,
>> + };
>> +
>> + int status = i2c_transfer(client->adapter, &msg, 1);
>> +
>> + return (status < 0) ? status : (msgbuf[1]|(msgbuf[0]<<8));
>> +}
>> +
>> +static int ina2xx_do_update(struct device *dev, int reg_mask)
>> {
>> struct ina2xx_data *data = dev_get_drvdata(dev);
>> struct i2c_client *client = data->client;
>> - int i, rv, retry;
>> + int i = 0, rv, retry;
>>
>> dev_dbg(&client->dev, "Starting ina2xx update\n");
>>
>> for (retry = 5; retry; retry--) {
>> - /* Read all registers */
>> - for (i = 0; i < data->config->registers; i++) {
>> - rv = i2c_smbus_read_word_swapped(client, i);
>> +
>> + /* Try to issue a shorter i2c message */
>> + if (reg_mask & (1 << data->last_reg)) {
>> + rv = __i2c_read_same_word(client);
>> if (rv < 0)
>> return rv;
>> - data->regs[i] = rv;
>> +
>> + reg_mask &= ~(1 << data->last_reg);
>> + data->regs[data->last_reg] = rv;
>> +
>> + dev_dbg(&client->dev, "%d, rv = %x, (last_reg)\n",
>> + data->last_reg,
>> + data->regs[data->last_reg]);
>> + }
>> +
>> + /* Check for remaining registers in mask. */
>> + while (reg_mask && i < data->config->registers) {
>> + if (reg_mask & (1L << i)) {
>> + rv = i2c_smbus_read_word_swapped(client, i);
>> + if (rv < 0)
>> + return rv;
>> + data->regs[i] = rv;
>> + data->last_reg = i;
>> +
>> + dev_dbg(&client->dev, "%d, rv = %x\n", i,
>> + data->regs[i]);
>> + }
>> + i++;
>> }
>>
>> /*
>> @@ -240,8 +289,6 @@ static int ina2xx_do_update(struct device *dev)
>> msleep(INA2XX_MAX_DELAY);
>> continue;
>> }
>> -
>> - data->last_updated = jiffies;
>> data->valid = 1;
>>
>> return 0;
>> @@ -256,22 +303,24 @@ static int ina2xx_do_update(struct device *dev)
>> return -ENODEV;
>> }
>>
>> -static struct ina2xx_data *ina2xx_update_device(struct device *dev)
>> +static struct ina2xx_data *ina2xx_update_device(struct device *dev,
>> + int reg_mask)
>> {
>> struct ina2xx_data *data = dev_get_drvdata(dev);
>> struct ina2xx_data *ret = data;
>> - unsigned long after;
>> int rv;
>>
>> mutex_lock(&data->update_lock);
>>
>> - after = data->last_updated + data->update_interval;
>> - if (time_after(jiffies, after) || !data->valid) {
>> - rv = ina2xx_do_update(dev);
>> - if (rv < 0)
>> - ret = ERR_PTR(rv);
>> + if (!data->valid) {
>> + reg_mask = 0xff; /* do all regs */
>> + data->last_reg = 0xff;
>> }
>>
>> + rv = ina2xx_do_update(dev, reg_mask);
>> + if (rv < 0)
>> + ret = ERR_PTR(rv);
>> +
>> mutex_unlock(&data->update_lock);
>> return ret;
>> }
>> @@ -316,7 +365,8 @@ static ssize_t ina2xx_show_value(struct device *dev,
>> struct device_attribute *da, char *buf)
>> {
>> struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
>> - struct ina2xx_data *data = ina2xx_update_device(dev);
>> + struct ina2xx_data *data = ina2xx_update_device(dev,
>> + BITPOS_TO_MASK(attr->index));
>>
>> if (IS_ERR(data))
>> return PTR_ERR(data);
>> @@ -329,7 +379,8 @@ static ssize_t ina2xx_set_shunt(struct device *dev,
>> struct device_attribute *da,
>> const char *buf, size_t count)
>> {
>> - struct ina2xx_data *data = ina2xx_update_device(dev);
>> + struct ina2xx_data *data = ina2xx_update_device(dev,
>> + BITPOS_TO_MASK(INA2XX_CONFIG));
>> unsigned long val;
>> int status;
>>
>> @@ -390,7 +441,8 @@ static ssize_t ina226_set_interval(struct device
>> *dev,
>> static ssize_t ina226_show_interval(struct device *dev,
>> struct device_attribute *da, char *buf)
>> {
>> - struct ina2xx_data *data = ina2xx_update_device(dev);
>> + struct ina2xx_data *data = ina2xx_update_device(dev,
>> + BITPOS_TO_MASK(INA2XX_CONFIG));
>>
>> if (IS_ERR(data))
>> return PTR_ERR(data);
>>
>
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