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Subject: Re: [PATCH 2/3] iio: adc: ti-ads8344: remove tx_buf from driver data
To:     Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Jonathan Cameron <jic23@kernel.org>
Cc:     Hartmut Knaack <knaack.h@gmx.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        Gregory CLEMENT <gregory.clement@bootlin.com>,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20200415212257.161238-1-alexandre.belloni@bootlin.com>
 <20200415212257.161238-3-alexandre.belloni@bootlin.com>
From:   Lars-Peter Clausen <lars@metafoo.de>
Message-ID: <3b3adb8b-24a0-acb8-7b03-d905733319d5@metafoo.de>
Date:   Thu, 16 Apr 2020 08:26:36 +0200
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On 4/15/20 11:22 PM, Alexandre Belloni wrote:
> There is no need to keep tx_buf around, it is only used for the conversion.
>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> ---
>   drivers/iio/adc/ti-ads8344.c | 18 ++++++------------
>   1 file changed, 6 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/iio/adc/ti-ads8344.c b/drivers/iio/adc/ti-ads8344.c
> index 6da50ea35217..9b2d3a8ea6bd 100644
> --- a/drivers/iio/adc/ti-ads8344.c
> +++ b/drivers/iio/adc/ti-ads8344.c
> @@ -22,13 +22,7 @@
>   struct ads8344 {
>   	struct spi_device *spi;
>   	struct regulator *reg;
> -	/*
> -	 * Lock protecting access to adc->tx_buff and rx_buff,
> -	 * especially from concurrent read on sysfs file.
> -	 */
> -	struct mutex lock;
> -
> -	u8 tx_buf ____cacheline_aligned;
> +	struct mutex lock; /* protect from concurrent conversions */
>   };
>   
>   #define ADS8344_VOLTAGE_CHANNEL(chan, si)				\
> @@ -77,13 +71,13 @@ static int ads8344_adc_conversion(struct ads8344 *adc, int channel,
>   	int ret;
>   	u8 buf[3];

spi_write() might use the buffer in a DMA transfer, so it can't be on 
the stack and needs to be in its own cacheline.

>   
> -	adc->tx_buf = ADS8344_START;
> +	buf[0] = ADS8344_START;
>   	if (!differential)
> -		adc->tx_buf |= ADS8344_SINGLE_END;
> -	adc->tx_buf |= ADS8344_CHANNEL(channel);
> -	adc->tx_buf |= ADS8344_CLOCK_INTERNAL;
> +		buf[0] |= ADS8344_SINGLE_END;
> +	buf[0] |= ADS8344_CHANNEL(channel);
> +	buf[0] |= ADS8344_CLOCK_INTERNAL;
>   
> -	ret = spi_write(spi, &adc->tx_buf, 1);
> +	ret = spi_write(spi, buf, 1);
>   	if (ret)
>   		return ret;
>