linux-kernel - Re: [PATCH] hwmon: (pmbus_core) Check adapter PEC support

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Date:   Fri, 4 Jun 2021 17:51:24 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Jean Delvare <jdelvare@...e.com>,
        Madhava Reddy Siddareddygari <msiddare@...co.com>,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (pmbus_core) Check adapter PEC support

On Fri, Jun 04, 2021 at 03:57:14PM +0200, Paul Menzel wrote:
> From: Madhava Reddy Siddareddygari <msiddare@...co.com>
> 
> Currently, for Packet Error Checking (PEC) only the controller
> is checked for support. This causes problems on the cisco-8000
> platform where a SMBUS transaction errors are observed. This is
> because PEC has to be enabled only if both controller and
> adapter support it.
> 
> Added code to check PEC capability for adapter and enable it
> only if both controller and adapter supports PEC.
> 
> Signed-off-by: Madhava Reddy Siddareddygari <msiddare@...co.com>
> [Upstream from SONiC https://github.com/Azure/sonic-linux-kernel/pull/215]
> Signed-off-by: Paul Menzel <pmenzel@...gen.mpg.de>
> ---
>  drivers/hwmon/pmbus/pmbus_core.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index bbd745178147..7fbd82b7560d 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -2214,11 +2214,13 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
>  		data->has_status_word = true;
>  	}
>  
> -	/* Enable PEC if the controller supports it */
> -	if (!(data->flags & PMBUS_NO_CAPABILITY)) {

What is the rationale for removing this check ?
AFAICS that will render the ibm-cffps driver unusable.

Guenter

> -		ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
> -		if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK))
> +	/* Enable PEC if the controller and bus supports it */
> +	ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
> +	if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK)) {
> +		if (i2c_check_functionality(client->adapter,
> +			I2C_FUNC_SMBUS_PEC)) {
>  			client->flags |= I2C_CLIENT_PEC;
> +		}
>  	}
>  
>  	/*
> -- 
> 2.32.0.rc2
>