linux-kernel - Re: [PATCH v2] staging: iio: adc: ad7816: add mutex to serialize SPI/GPIO operations

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Message-ID: <aLWaxoBLEVWlfzN7@stanley.mountain>
Date: Mon, 1 Sep 2025 16:08:22 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Mohammad Amin Hosseini <moahmmad.hosseinii@...il.com>
Cc: linux-iio@...r.kernel.org, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	jic23@...nel.org, lars@...afoo.de, Michael.Hennerich@...log.com,
	dlechner@...libre.com, nuno.sa@...log.com, andy@...nel.org
Subject: Re: [PATCH v2] staging: iio: adc: ad7816: add mutex to serialize
 SPI/GPIO operations

On Mon, Sep 01, 2025 at 10:24:45AM +0330, Mohammad Amin Hosseini wrote:
> @@ -200,7 +204,9 @@ static ssize_t ad7816_store_channel(struct device *dev,
>  		return -EINVAL;
>  	}
>  
> +	mutex_lock(&chip->io_lock);
>  	chip->channel_id = data;
> +	mutex_unlock(&chip->io_lock);
>  
>  	return len;
>  }

Unrelated, but what is the point of setting chip->channel_id to
AD7816_CS_MASK?  The only time where that is used is in
ad7816_spi_read() when we do:

	ret = spi_write(spi_dev, &chip->channel_id, sizeof(chip->channel_id));

So it's something in the hardware spec, I guess, but it isn't
documented.

regards,
dan carpenter