Re: [PATCH 3/3] hwmon: pmbus: Fix -EIO seen on pli1209

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

On Thu, Aug 17, 2023 at 11:25:26AM +0200, Naresh Solanki wrote:
> From: Patrick Rudolph <patrick.rudolph@9elements.com>
> 
> After doing performance optimizations the pli1209 driver failed to
> probe with a probabilty of 2%. It wasn't able to read the PMBUS_OPERATION
> register due to an -EIO error.
> 
> An investigation showed that the PLI1209 takes 230 usec to execute the
> CLEAR_FAULTS command. During that time it's busy and NACKs all requests
> on the SMBUS interface. It also NACKs reads on PMBUS_STATUS_BYTE
> making it impossible to poll the BUSY flag.
> 
> Add a custom write_data function to just wait for not BUSY unconditionally
> after sending a CLEAR_FAULTS command.
> 
> TEST: Verified using an I2C bus analyser that no more NACKs are seen after
>       sending a CLEAR_FAULTS command.
> 
> Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
> Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/pmbus/pli1209bc.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/hwmon/pmbus/pli1209bc.c b/drivers/hwmon/pmbus/pli1209bc.c
> index 7d8bd3167b21..c95433790b11 100644
> --- a/drivers/hwmon/pmbus/pli1209bc.c
> +++ b/drivers/hwmon/pmbus/pli1209bc.c
> @@ -5,6 +5,7 @@
>   * Copyright (c) 2022 9elements GmbH
>   */
>  
> +#include <linux/delay.h>
>  #include <linux/i2c.h>
>  #include <linux/module.h>
>  #include <linux/pmbus.h>
> @@ -53,6 +54,30 @@ static int pli1209bc_read_word_data(struct i2c_client *client, int page,
>  	}
>  }
>  
> +static int pli1209bc_write_byte(struct i2c_client *client, int page, u8 reg)
> +{
> +	int ret;
> +
> +	switch (reg) {
> +	case PMBUS_CLEAR_FAULTS:
> +		ret = pmbus_write_byte(client, page, reg);
> +		/*
> +		 * PLI1209 takes 230 usec to execute the CLEAR_FAULTS command.
> +		 * During that time it's busy and NACKs all requests on the
> +		 * SMBUS interface. It also NACKs reads on PMBUS_STATUS_BYTE
> +		 * making it impossible to poll the BUSY flag.
> +		 *
> +		 * Just wait for not BUSY unconditionally.
> +		 */
> +		usleep_range(250, 300);
> +		break;
> +	default:
> +		ret = -ENODATA;
> +		break;
> +	}
> +	return ret;
> +}
> +
>  #if IS_ENABLED(CONFIG_SENSORS_PLI1209BC_REGULATOR)
>  static const struct regulator_desc pli1209bc_reg_desc = {
>  	.name = "vout2",
> @@ -102,6 +127,7 @@ static struct pmbus_driver_info pli1209bc_info = {
>  	    | PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP
>  	    | PMBUS_HAVE_STATUS_IOUT | PMBUS_HAVE_STATUS_INPUT,
>  	.read_word_data = pli1209bc_read_word_data,
> +	.write_byte = pli1209bc_write_byte,
>  #if IS_ENABLED(CONFIG_SENSORS_PLI1209BC_REGULATOR)
>  	.num_regulators = 1,
>  	.reg_desc = &pli1209bc_reg_desc,