linux-kernel - Re: [PATCH] iio: amplifiers: ada4250: use DMA-safe memory for regmap_bulk

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Message-ID: <20250421115924.682f52ee@jic23-huawei>
Date: Mon, 21 Apr 2025 11:59:24 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Antoniu Miclaus <antoniu.miclaus@...log.com>, Lars-Peter Clausen
 <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, Nuno
 Sá <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: amplifiers: ada4250: use DMA-safe memory for
 regmap_bulk_read()

On Fri, 18 Apr 2025 13:16:13 -0500
David Lechner <dlechner@...libre.com> wrote:

> Use DMA-safe memory instead of stack-allocated memory for the call to
> regmap_bulk_read() in the ada4250_init() function as this could be used
> directly by a SPI controller.
> 
> Also remove unnecessary use of get_unaligned_le16() and explicitly
> include linux/types.h e.g. for __le16 while we are fixing this up.
> 
> Fixes: 28b4c30bfa5f ("iio: amplifiers: ada4250: add support for ADA4250")
> Signed-off-by: David Lechner <dlechner@...libre.com>
Let's wait and see if Mark has a view on this.  The switch to an __le16 is
good either way.

Jonathan

> ---
>  drivers/iio/amplifiers/ada4250.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/amplifiers/ada4250.c b/drivers/iio/amplifiers/ada4250.c
> index 74f8429d652b17b4d1f38366e23ce6a2b3e9b218..f81438460aa51ce30f8f605c60ee5be5c8c251d3 100644
> --- a/drivers/iio/amplifiers/ada4250.c
> +++ b/drivers/iio/amplifiers/ada4250.c
> @@ -13,8 +13,7 @@
>  #include <linux/regmap.h>
>  #include <linux/regulator/consumer.h>
>  #include <linux/spi/spi.h>
> -
> -#include <linux/unaligned.h>
> +#include <linux/types.h>
>  
>  /* ADA4250 Register Map */
>  #define ADA4250_REG_GAIN_MUX        0x00
> @@ -63,6 +62,7 @@ struct ada4250_state {
>  	u8			gain;
>  	int			offset_uv;
>  	bool			refbuf_en;
> +	__le16			reg_val_16 __aligned(IIO_DMA_MINALIGN);
>  };
>  
>  /* ADA4250 Current Bias Source Settings: Disabled, Bandgap Reference, AVDD */
> @@ -301,7 +301,6 @@ static int ada4250_init(struct ada4250_state *st)
>  {
>  	int ret;
>  	u16 chip_id;
> -	u8 data[2] __aligned(8) = {};
>  	struct spi_device *spi = st->spi;
>  
>  	st->refbuf_en = device_property_read_bool(&spi->dev, "adi,refbuf-enable");
> @@ -326,11 +325,12 @@ static int ada4250_init(struct ada4250_state *st)
>  	if (ret)
>  		return ret;
>  
> -	ret = regmap_bulk_read(st->regmap, ADA4250_REG_CHIP_ID, data, 2);
> +	ret = regmap_bulk_read(st->regmap, ADA4250_REG_CHIP_ID, &st->reg_val_16,
> +			       sizeof(st->reg_val_16));
>  	if (ret)
>  		return ret;
>  
> -	chip_id = get_unaligned_le16(data);
> +	chip_id = le16_to_cpu(st->reg_val_16);
>  
>  	if (chip_id != ADA4250_CHIP_ID) {
>  		dev_err(&spi->dev, "Invalid chip ID.\n");
> 
> ---
> base-commit: aff301f37e220970c2f301b5c65a8bfedf52058e
> change-id: 20250418-iio-amplifiers-ada4250-simplify-data-buffer-in-init-93ebb1344295
> 
> Best regards,