linux-kernel - Re: [PATCH] hwmon: sparx5: Fix initial reading of temperature

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Message-ID: <8ca270c9-5561-3176-61cf-7a9fbee10d1f@roeck-us.net>
Date:   Thu, 3 Sep 2020 06:52:09 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Lars Povlsen <lars.povlsen@...rochip.com>
Cc:     Jean Delvare <jdelvare@...e.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        linux-hwmon@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: sparx5: Fix initial reading of temperature

On 9/3/20 6:47 AM, Lars Povlsen wrote:
> If the temperature is read before the internal calibration is
> completed, the driver returns -EIO. Instead it should return -EAGAIN
> to encourage repeating the operation.
> 
> Signed-off-by: Lars Povlsen <lars.povlsen@...rochip.com>
> ---
>  drivers/hwmon/sparx5-temp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/sparx5-temp.c b/drivers/hwmon/sparx5-temp.c
> index 1a2b1026b026..98be48e3a22a 100644
> --- a/drivers/hwmon/sparx5-temp.c
> +++ b/drivers/hwmon/sparx5-temp.c
> @@ -56,7 +56,7 @@ static int s5_read(struct device *dev, enum hwmon_sensor_types type,
>  	case hwmon_temp_input:
>  		stat = readl_relaxed(hwmon->base + TEMP_STAT);
>  		if (!(stat & TEMP_STAT_VALID))
> -			return -EIO;
> +			return -EAGAIN;

The problem is that this may result in a hard loop and effectively hang the system,
or at least the calling process. It may be better to return -ENODATA in this situation.

Guenter

>  		value = stat & TEMP_STAT_TEMP;
>  		/*
>  		 * From register documentation:
> --
> 2.27.0
>