linux-kernel - Re: [PATCH 3/3] hwmon: bt1-pvt: Wait for the completion with timeout

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Date:   Fri, 2 Oct 2020 09:15:59 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Jean Delvare <jdelvare@...e.com>,
        Maxim Kaurkin <maxim.kaurkin@...kalelectronics.ru>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        linux-mips@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] hwmon: bt1-pvt: Wait for the completion with timeout

On Sun, Sep 20, 2020 at 02:09:23PM +0300, Serge Semin wrote:
> If the PVT sensor is suddenly powered down while a caller is waiting for
> the conversion completion, the request won't be finished and the task will
> hang up on this procedure until the power is back up again. Let's call the
> wait_for_completion_timeout() method instead to prevent that. The cached
> timeout is exactly what we need to predict for how long conversion could
> normally last.
> 
> Fixes: 87976ce2825d ("hwmon: Add Baikal-T1 PVT sensor driver")
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/bt1-pvt.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/bt1-pvt.c b/drivers/hwmon/bt1-pvt.c
> index 2600426a3b21..3e1d56585b91 100644
> --- a/drivers/hwmon/bt1-pvt.c
> +++ b/drivers/hwmon/bt1-pvt.c
> @@ -477,6 +477,7 @@ static int pvt_read_data(struct pvt_hwmon *pvt, enum pvt_sensor_type type,
>  			 long *val)
>  {
>  	struct pvt_cache *cache = &pvt->cache[type];
> +	unsigned long timeout;
>  	u32 data;
>  	int ret;
>  
> @@ -500,7 +501,14 @@ static int pvt_read_data(struct pvt_hwmon *pvt, enum pvt_sensor_type type,
>  	pvt_update(pvt->regs + PVT_INTR_MASK, PVT_INTR_DVALID, 0);
>  	pvt_update(pvt->regs + PVT_CTRL, PVT_CTRL_EN, PVT_CTRL_EN);
>  
> -	wait_for_completion(&cache->conversion);
> +	/*
> +	 * Wait with timeout since in case if the sensor is suddenly powered
> +	 * down the request won't be completed and the caller will hang up on
> +	 * this procedure until the power is back up again. Multiply the
> +	 * timeout by the factor of two to prevent a false timeout.
> +	 */
> +	timeout = 2 * usecs_to_jiffies(ktime_to_us(pvt->timeout));
> +	ret = wait_for_completion_timeout(&cache->conversion, timeout);
>  
>  	pvt_update(pvt->regs + PVT_CTRL, PVT_CTRL_EN, 0);
>  	pvt_update(pvt->regs + PVT_INTR_MASK, PVT_INTR_DVALID,
> @@ -510,6 +518,9 @@ static int pvt_read_data(struct pvt_hwmon *pvt, enum pvt_sensor_type type,
>  
>  	mutex_unlock(&pvt->iface_mtx);
>  
> +	if (!ret)
> +		return -ETIMEDOUT;
> +
>  	if (type == PVT_TEMP)
>  		*val = pvt_calc_poly(&poly_N_to_temp, data);
>  	else