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Message-ID: <56259997.6080706@roeck-us.net>
Date: Mon, 19 Oct 2015 18:32:07 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Marc Titinger <mtitinger@...libre.com>, 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 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.
>
I really dislike that complexity. Maybe we should drop caching entirely
in this driver ? Maybe even convert it to use regmap ?
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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