linux-kernel - Re: [PATCH 5/5] iio: adc: ad7380: use spi_optimize

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Message-ID: <c06dfa1ecf88b07ef467ad7c08667d0cab400613.camel@gmail.com>
Date: Tue, 13 Feb 2024 10:51:15 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: David Lechner <dlechner@...libre.com>, Mark Brown <broonie@...nel.org>
Cc: Martin Sperl <kernel@...tin.sperl.org>, David Jander
 <david@...tonic.nl>,  Jonathan Cameron <jic23@...nel.org>, Michael
 Hennerich <michael.hennerich@...log.com>, Nuno Sá
 <nuno.sa@...log.com>, Alain Volmat <alain.volmat@...s.st.com>, Maxime
 Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>,  linux-spi@...r.kernel.org,
 linux-kernel@...r.kernel.org,  linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org,  linux-iio@...r.kernel.org
Subject: Re: [PATCH 5/5] iio: adc: ad7380: use spi_optimize_message()

On Mon, 2024-02-12 at 17:26 -0600, David Lechner wrote:
> This modifies the ad7380 ADC driver to use spi_optimize_message() to
> optimize the SPI message for the buffered read operation. Since buffered
> reads reuse the same SPI message for each read, this can improve
> performance by reducing the overhead of setting up some parts the SPI
> message in each spi_sync() call.
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
> ---
>  drivers/iio/adc/ad7380.c | 52 +++++++++++++++++++++++++++++++++++++++++------
> -
>  1 file changed, 45 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
> index abd746aef868..5c5d2642a474 100644
> --- a/drivers/iio/adc/ad7380.c
> +++ b/drivers/iio/adc/ad7380.c
> @@ -133,6 +133,7 @@ struct ad7380_state {
>  	struct spi_device *spi;
>  	struct regulator *vref;
>  	struct regmap *regmap;
> +	struct spi_message *msg;
>  	/*
>  	 * DMA (thus cache coherency maintenance) requires the
>  	 * transfer buffers to live in their own cache lines.
> @@ -231,19 +232,55 @@ static int ad7380_debugfs_reg_access(struct iio_dev
> *indio_dev, u32 reg,
>  	return ret;
>  }
>  
> +static int ad7380_buffer_preenable(struct iio_dev *indio_dev)
> +{
> +	struct ad7380_state *st = iio_priv(indio_dev);
> +	struct spi_transfer *xfer;
> +	int ret;
> +
> +	st->msg = spi_message_alloc(1, GFP_KERNEL);
> +	if (!st->msg)
> +		return -ENOMEM;
> +
> +	xfer = list_first_entry(&st->msg->transfers, struct spi_transfer,
> +				transfer_list);
> +
> +	xfer->bits_per_word = st->chip_info->channels[0].scan_type.realbits;
> +	xfer->len = 4;
> +	xfer->rx_buf = st->scan_data.raw;
> +
> +	ret = spi_optimize_message(st->spi, st->msg);
> +	if (ret) {
> +		spi_message_free(st->msg);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static int ad7380_buffer_postdisable(struct iio_dev *indio_dev)
> +{
> +	struct ad7380_state *st = iio_priv(indio_dev);
> +
> +	spi_unoptimize_message(st->msg);
> +	spi_message_free(st->msg);
> +
> +	return 0;
> +}
> +

Not such a big deal but unless I'm missing something we could have the
spi_message (+ the transfer) statically allocated in struct ad7380_state and do
the optimize only once at probe (naturally with proper devm action for
unoptimize). Then we would not need to this for every buffer enable + disable. I
know in terms of performance it won't matter but it would be less code I guess.

Am I missing something?

- Nuno Sá