linux-kernel - Re: [PATCH] hwmon: da9052: Synchronize access with mfd

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Message-ID: <930d27f3-46f8-2e7a-5028-b593f4fe84a3@roeck-us.net>
Date:   Mon, 11 May 2020 09:51:25 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>,
        Support Opensource <support.opensource@...semi.com>,
        Jean Delvare <jdelvare@...e.com>
Cc:     Lee Jones <lee.jones@...aro.org>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...labora.com,
        Samu Nuutamo <samu.nuutamo@...cit.fi>
Subject: Re: [PATCH] hwmon: da9052: Synchronize access with mfd

On 5/11/20 4:02 AM, Sebastian Reichel wrote:
> From: Samu Nuutamo <samu.nuutamo@...cit.fi>
> 
> When tsi-as-adc is configured it is possible for in7[0123]_input read to
> return an incorrect value if a concurrent read to in[456]_input is
> performed. This is caused by a concurrent manipulation of the mux
> channel without proper locking as hwmon and mfd use different locks for
> synchronization.
> 
> Switch hwmon to use the same lock as mfd when accessing the TSI channel.
> 
> Fixes: 4f16cab19a3d5 ("hwmon: da9052: Add support for TSI channel")
> Signed-off-by: Samu Nuutamo <samu.nuutamo@...cit.fi>
> [rebase to current master, reword commit message slightly]
> Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>

Have you explored calling da9052_adc_manual_read() instead ?
At the very least we should have a comment explaining why that
isn't feasible.

Thanks,
Guenter

> ---
>  drivers/hwmon/da9052-hwmon.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/da9052-hwmon.c b/drivers/hwmon/da9052-hwmon.c
> index 53b517dbe7e6..4af2fc309c28 100644
> --- a/drivers/hwmon/da9052-hwmon.c
> +++ b/drivers/hwmon/da9052-hwmon.c
> @@ -244,9 +244,9 @@ static ssize_t da9052_tsi_show(struct device *dev,
>  	int channel = to_sensor_dev_attr(devattr)->index;
>  	int ret;
>  
> -	mutex_lock(&hwmon->hwmon_lock);
> +	mutex_lock(&hwmon->da9052->auxadc_lock);
>  	ret = __da9052_read_tsi(dev, channel);
> -	mutex_unlock(&hwmon->hwmon_lock);
> +	mutex_unlock(&hwmon->da9052->auxadc_lock);
>  
>  	if (ret < 0)
>  		return ret;
>