linux-kernel - Re: [PATCH v4 2/7] iio: adc: ad4695: use u16 for buffer elements

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Message-ID: <48336225-0e43-46b5-bfc0-34ca8e6a4399@baylibre.com>
Date: Mon, 28 Apr 2025 16:33:21 -0400
From: Trevor Gamblin <tgamblin@...libre.com>
To: David Lechner <dlechner@...libre.com>, Jonathan Cameron
 <jic23@...nel.org>, Nuno Sá <nuno.sa@...log.com>,
 Andy Shevchenko <andy@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Eugen Hristev <eugen.hristev@...aro.org>,
 Nicolas Ferre <nicolas.ferre@...rochip.com>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 Claudiu Beznea <claudiu.beznea@...on.dev>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 2/7] iio: adc: ad4695: use u16 for buffer elements


On 2025-04-28 16:23, David Lechner wrote:
> Change the type of the buffer elements to u16 since we currently only
> support 16-bit word size. The code was originally written to also allow
> for 32-bit word size when oversampling is enabled, but so far,
> oversampling is only implemented when using SPI offload and therefore
> doesn't use this buffer.
>
> AD4695_MAX_CHANNEL_SIZE macro is dropped since it no longer adds any
> value.
>
> AD4695_MAX_CHANNELS + 2 is changed to AD4695_MAX_CHANNELS + 1 because
> previously we were overallocating. AD4695_MAX_CHANNELS is the number of
> of voltage channels and + 1 is for the temperature channel.
>
> Signed-off-by: David Lechner <dlechner@...libre.com>
Reviewed-by: Trevor Gamblin <tgamblin@...libre.com>
> ---
>   drivers/iio/adc/ad4695.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/iio/adc/ad4695.c b/drivers/iio/adc/ad4695.c
> index 68c6625db0d75f4cade7cb029e94191118dbcaa0..0c633d43e480d5404074e9fa35f1d330b448f0a2 100644
> --- a/drivers/iio/adc/ad4695.c
> +++ b/drivers/iio/adc/ad4695.c
> @@ -106,8 +106,6 @@
>   
>   /* Max number of voltage input channels. */
>   #define AD4695_MAX_CHANNELS		16
> -/* Max size of 1 raw sample in bytes. */
> -#define AD4695_MAX_CHANNEL_SIZE		2
>   
>   enum ad4695_in_pair {
>   	AD4695_IN_PAIR_REFGND,
> @@ -162,8 +160,8 @@ struct ad4695_state {
>   	struct spi_transfer buf_read_xfer[AD4695_MAX_CHANNELS * 2 + 3];
>   	struct spi_message buf_read_msg;
>   	/* Raw conversion data received. */
> -	u8 buf[ALIGN((AD4695_MAX_CHANNELS + 2) * AD4695_MAX_CHANNEL_SIZE,
> -		     sizeof(s64)) + sizeof(s64)] __aligned(IIO_DMA_MINALIGN);
> +	u16 buf[ALIGN((AD4695_MAX_CHANNELS + 1) * sizeof(u16),
> +		      sizeof(s64)) + sizeof(s64)] __aligned(IIO_DMA_MINALIGN);
>   	u16 raw_data;
>   	/* Commands to send for single conversion. */
>   	u16 cnv_cmd;
> @@ -660,9 +658,8 @@ static int ad4695_buffer_preenable(struct iio_dev *indio_dev)
>   	iio_for_each_active_channel(indio_dev, bit) {
>   		xfer = &st->buf_read_xfer[num_xfer];
>   		xfer->bits_per_word = 16;
> -		xfer->rx_buf = &st->buf[rx_buf_offset];
> +		xfer->rx_buf = &st->buf[rx_buf_offset++];
>   		xfer->len = 2;
> -		rx_buf_offset += xfer->len;
>   
>   		if (bit == temp_chan_bit) {
>   			temp_en = 1;
>