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References: <20200415212257.161238-1-alexandre.belloni@bootlin.com> <20200415212257.161238-3-alexandre.belloni@bootlin.com>
In-Reply-To: <20200415212257.161238-3-alexandre.belloni@bootlin.com>
From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 17 Apr 2020 13:24:57 +0300
Message-ID: <CAHp75VcHRYLqk_b6H6TXqer98c6ZzSKctW=CbMvHzdThPxjfgQ@mail.gmail.com>
Subject: Re: [PATCH 2/3] iio: adc: ti-ads8344: remove tx_buf from driver data
To:     Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc:     Jonathan Cameron <jic23@kernel.org>,
        Hartmut Knaack <knaack.h@gmx.de>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        Gregory CLEMENT <gregory.clement@bootlin.com>,
        linux-iio <linux-iio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Apr 16, 2020 at 4:08 AM Alexandre Belloni
<alexandre.belloni@bootlin.com> wrote:
>
> There is no need to keep tx_buf around, it is only used for the conversion.
>

As Lars said. And some SPI controllers may want to DMA even one byte, so, NAK.


> 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];
>
> -       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;
>
> --
> 2.25.2
>


-- 
With Best Regards,
Andy Shevchenko