2020-04-16 01:10:03

by Alexandre Belloni

Subject: [PATCH 2/3] iio: adc: ti-ads8344: remove tx_buf from driver data

There is no need to keep tx_buf around, it is only used for the conversion.

Signed-off-by: Alexandre Belloni <[email protected]>
---
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

2020-04-16 06:30:44

by Lars-Peter Clausen

Subject: Re: [PATCH 2/3] iio: adc: ti-ads8344: remove tx_buf from driver data

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 <[email protected]>
> ---
> 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;
>

2020-04-17 10:28:34

by Andy Shevchenko

Subject: Re: [PATCH 2/3] iio: adc: ti-ads8344: remove tx_buf from driver data

On Thu, Apr 16, 2020 at 4:08 AM Alexandre Belloni
<[email protected]> 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 <[email protected]>
> ---
> 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