Re: [PATCH 2/3] hwmon: (tps23861) reduce count of i2c transactions for port_status

[Guenter Roeck <linux@roeck-us.net>]

On Mon, Sep 05, 2022 at 09:28:05AM -0500, Alexandru Gagniuc wrote:
> When reading the 'port_status' debugfs entry, some I2C registers were
> read more than once. This looks inefficient in an I2C trace.
> 
> To reduce I2C traffic, update tps23861_port_status_show() to only read
> each register once. Indexing the port number from 0 instead of 1 also
> allows simplifying things a bit, resulting in a negative line count.

"resulting in a negative line count"

That took me a while to understand. Please rephrase or drop.

> 
> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
> ---
>  drivers/hwmon/tps23861.c | 75 ++++++++++++----------------------------
>  1 file changed, 22 insertions(+), 53 deletions(-)
> 
> diff --git a/drivers/hwmon/tps23861.c b/drivers/hwmon/tps23861.c
> index f7c59ff7ae8e..0dbd12060b50 100644
> --- a/drivers/hwmon/tps23861.c
> +++ b/drivers/hwmon/tps23861.c
> @@ -372,29 +372,12 @@ static const struct hwmon_chip_info tps23861_chip_info = {
>  	.info = tps23861_info,
>  };
>  
> -static char *tps23861_port_operating_mode(struct tps23861_data *data, int port)
> +static char *port_operating_mode_string(uint8_t mode_reg, unsigned int port)
>  {
> -	unsigned int regval;
> -	int mode;
> -
> -	regmap_read(data->regmap, OPERATING_MODE, &regval);
> +	unsigned int mode = ~0;
>  
> -	switch (port) {
> -	case 1:
> -		mode = FIELD_GET(OPERATING_MODE_PORT_1_MASK, regval);
> -		break;
> -	case 2:
> -		mode = FIELD_GET(OPERATING_MODE_PORT_2_MASK, regval);
> -		break;
> -	case 3:
> -		mode = FIELD_GET(OPERATING_MODE_PORT_3_MASK, regval);
> -		break;
> -	case 4:
> -		mode = FIELD_GET(OPERATING_MODE_PORT_4_MASK, regval);
> -		break;
> -	default:
> -		mode = -EINVAL;
> -	}
> +	if (port < TPS23861_NUM_PORTS)
> +		mode = (mode_reg >> (2 * port)) & OPERATING_MODE_PORT_1_MASK;
>  
>  	switch (mode) {
>  	case OPERATING_MODE_OFF:
> @@ -410,15 +393,9 @@ static char *tps23861_port_operating_mode(struct tps23861_data *data, int port)
>  	}
>  }
>  
> -static char *tps23861_port_detect_status(struct tps23861_data *data, int port)
> +static char *port_detect_status_string(uint8_t status_reg)
>  {
> -	unsigned int regval;
> -
> -	regmap_read(data->regmap,
> -		    PORT_1_STATUS + (port - 1),
> -		    &regval);
> -
> -	switch (FIELD_GET(PORT_STATUS_DETECT_MASK, regval)) {
> +	switch (FIELD_GET(PORT_STATUS_DETECT_MASK, status_reg)) {
>  	case PORT_DETECT_UNKNOWN:
>  		return "Unknown device";
>  	case PORT_DETECT_SHORT:
> @@ -448,15 +425,9 @@ static char *tps23861_port_detect_status(struct tps23861_data *data, int port)
>  	}
>  }
>  
> -static char *tps23861_port_class_status(struct tps23861_data *data, int port)
> +static char *port_class_status_string(uint8_t status_reg)
>  {
> -	unsigned int regval;
> -
> -	regmap_read(data->regmap,
> -		    PORT_1_STATUS + (port - 1),
> -		    &regval);
> -
> -	switch (FIELD_GET(PORT_STATUS_CLASS_MASK, regval)) {
> +	switch (FIELD_GET(PORT_STATUS_CLASS_MASK, status_reg)) {
>  	case PORT_CLASS_UNKNOWN:
>  		return "Unknown";
>  	case PORT_CLASS_RESERVED:
> @@ -479,16 +450,9 @@ static char *tps23861_port_class_status(struct tps23861_data *data, int port)
>  	}
>  }
>  
> -static char *tps23861_port_poe_plus_status(struct tps23861_data *data, int port)
> +static char *port_poe_plus_status_string(uint8_t poe_plus, unsigned int port)
>  {
> -	unsigned int regval;
> -
> -	regmap_read(data->regmap, POE_PLUS, &regval);
> -
> -	if (BIT(port + 3) & regval)
> -		return "Yes";
> -	else
> -		return "No";
> +	return (BIT(port + 4) & poe_plus) ? "Yes" : "No";
>  }
>  
>  static int tps23861_port_resistance(struct tps23861_data *data, int port)
> @@ -497,7 +461,7 @@ static int tps23861_port_resistance(struct tps23861_data *data, int port)
>  	__le16 regval;
>  
>  	regmap_bulk_read(data->regmap,
> -			 PORT_1_RESISTANCE_LSB + PORT_N_RESISTANCE_LSB_OFFSET * (port - 1),
> +			 PORT_1_RESISTANCE_LSB + PORT_N_RESISTANCE_LSB_OFFSET * port,
>  			 &regval,
>  			 2);
>  
> @@ -517,14 +481,19 @@ static int tps23861_port_resistance(struct tps23861_data *data, int port)
>  static int tps23861_port_status_show(struct seq_file *s, void *data)
>  {
>  	struct tps23861_data *priv = s->private;
> -	int i;
> +	unsigned int i, mode, poe_plus, status;
> +
> +	regmap_read(priv->regmap, OPERATING_MODE, &mode);
> +	regmap_read(priv->regmap, POE_PLUS, &poe_plus);
> +
> +	for (i = 0; i < TPS23861_NUM_PORTS; i++) {
> +		regmap_read(priv->regmap, PORT_1_STATUS + i, &status);
>  
> -	for (i = 1; i < TPS23861_NUM_PORTS + 1; i++) {
>  		seq_printf(s, "Port: \t\t%d\n", i);

This changes the port number output from 1..4 to 0..3.
Why ? I can understand the code change, but that doesn't mean
the output has to change as well.

Thanks,
Guenter

> -		seq_printf(s, "Operating mode: %s\n", tps23861_port_operating_mode(priv, i));
> -		seq_printf(s, "Detected: \t%s\n", tps23861_port_detect_status(priv, i));
> -		seq_printf(s, "Class: \t\t%s\n", tps23861_port_class_status(priv, i));
> -		seq_printf(s, "PoE Plus: \t%s\n", tps23861_port_poe_plus_status(priv, i));
> +		seq_printf(s, "Operating mode: %s\n", port_operating_mode_string(mode, i));
> +		seq_printf(s, "Detected: \t%s\n", port_detect_status_string(status));
> +		seq_printf(s, "Class: \t\t%s\n", port_class_status_string(status));
> +		seq_printf(s, "PoE Plus: \t%s\n", port_poe_plus_status_string(poe_plus, i));
>  		seq_printf(s, "Resistance: \t%d\n", tps23861_port_resistance(priv, i));
>  		seq_putc(s, '\n');
>  	}