linux-kernel - Re: [PATCH] iio: adc: ad7944: drop bits_per

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Message-ID: <1f6116071b20846d07406a613d77fd45e5353690.camel@gmail.com>
Date: Tue, 01 Apr 2025 10:11:40 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: David Lechner <dlechner@...libre.com>, Jonathan Cameron
 <jic23@...nel.org>, 	linux-iio@...r.kernel.org
Cc: Michael Hennerich <michael.hennerich@...log.com>, Nuno
 Sá
	 <nuno.sa@...log.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: ad7944: drop bits_per_word hack

On Mon, 2025-03-31 at 14:29 -0500, David Lechner wrote:
> Remove setting bits_per_word in SPI xfers without data. The shortcoming
> that this was working around was fixed in the SPI controller driver, so
> it is no longer necessary. And we don't need this to be cargo-culted to
> new drivers.
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
> ---

Reviewed-by: Nuno Sá <nuno.sa@...log.com>

>  drivers/iio/adc/ad7944.c | 11 -----------
>  1 file changed, 11 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c
> index
> 2f949fe5587318957f2e423029294ced0a6f803d..70f313545af2393a625ae2ec3c2cff2e2915
> 3ffb 100644
> --- a/drivers/iio/adc/ad7944.c
> +++ b/drivers/iio/adc/ad7944.c
> @@ -189,11 +189,6 @@ static int ad7944_3wire_cs_mode_init_msg(struct device
> *dev, struct ad7944_adc *
>  						   : adc->timing_spec-
> >conv_ns;
>  	struct spi_transfer *xfers = adc->xfers;
>  
> -	/*
> -	 * NB: can get better performance from some SPI controllers if we use
> -	 * the same bits_per_word in every transfer.
> -	 */
> -	xfers[0].bits_per_word = chan->scan_type.realbits;
>  	/*
>  	 * CS is tied to CNV and we need a low to high transition to start
> the
>  	 * conversion, so place CNV low for t_QUIET to prepare for this.
> @@ -208,7 +203,6 @@ static int ad7944_3wire_cs_mode_init_msg(struct device
> *dev, struct ad7944_adc *
>  	xfers[1].cs_off = 1;
>  	xfers[1].delay.value = t_conv_ns;
>  	xfers[1].delay.unit = SPI_DELAY_UNIT_NSECS;
> -	xfers[1].bits_per_word = chan->scan_type.realbits;
>  
>  	/* Then we can read the data during the acquisition phase */
>  	xfers[2].rx_buf = &adc->sample.raw;
> @@ -227,11 +221,6 @@ static int ad7944_4wire_mode_init_msg(struct device *dev,
> struct ad7944_adc *adc
>  						   : adc->timing_spec-
> >conv_ns;
>  	struct spi_transfer *xfers = adc->xfers;
>  
> -	/*
> -	 * NB: can get better performance from some SPI controllers if we use
> -	 * the same bits_per_word in every transfer.
> -	 */
> -	xfers[0].bits_per_word = chan->scan_type.realbits;
>  	/*
>  	 * CS has to be high for full conversion time to avoid triggering the
>  	 * busy indication.
> 
> ---
> base-commit: f8ffc92ae9052e6615896052f0c5b808bfc17520
> change-id: 20250331-iio-adc-ad7944-drop-bits_per_word-hack-a71b2d51fa3f
> 
> Best regards,