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Message-ID: <e03968102b92b3711808eb532685bc9e05fc3c8d.camel@gmail.com>
Subject: Re: [PATCH 5/5] iio: adc: ad7380: use spi_optimize_message()
From: Nuno =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>
To: David Lechner <dlechner@baylibre.com>
Cc: Mark Brown <broonie@kernel.org>, Martin Sperl <kernel@martin.sperl.org>,
  David Jander <david@protonic.nl>, Jonathan Cameron <jic23@kernel.org>,
 Michael Hennerich <michael.hennerich@analog.com>, Nuno
 =?ISO-8859-1?Q?S=E1?= <nuno.sa@analog.com>,  Alain Volmat
 <alain.volmat@foss.st.com>, Maxime Coquelin <mcoquelin.stm32@gmail.com>,
 Alexandre Torgue <alexandre.torgue@foss.st.com>, linux-spi@vger.kernel.org,
  linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, 
 linux-arm-kernel@lists.infradead.org, linux-iio@vger.kernel.org
Date: Tue, 13 Feb 2024 17:08:19 +0100
In-Reply-To: <CAMknhBEU=iMzpE_P0KePL4cZZktBOGHRXaEox5a7XcVjXDT+Dg@mail.gmail.com>
References: 
	<20240212-mainline-spi-precook-message-v1-0-a2373cd72d36@baylibre.com>
	 <20240212-mainline-spi-precook-message-v1-5-a2373cd72d36@baylibre.com>
	 <c06dfa1ecf88b07ef467ad7c08667d0cab400613.camel@gmail.com>
	 <CAMknhBEU=iMzpE_P0KePL4cZZktBOGHRXaEox5a7XcVjXDT+Dg@mail.gmail.com>
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On Tue, 2024-02-13 at 09:27 -0600, David Lechner wrote:
> On Tue, Feb 13, 2024 at 3:47=E2=80=AFAM Nuno S=C3=A1 <noname.nuno@gmail.c=
om> wrote:
> >=20
> > 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 buffe=
red
> > > 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.
> > >=20
> > > Signed-off-by: David Lechner <dlechner@baylibre.com>
> > > ---
> > > =C2=A0drivers/iio/adc/ad7380.c | 52 +++++++++++++++++++++++++++++++++=
++++++++--
> > > ----
> > > -
> > > =C2=A01 file changed, 45 insertions(+), 7 deletions(-)
> > >=20
> > > 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 {
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct spi_device *spi;
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct regulator *vref;
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct regmap *regmap;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 struct spi_message *msg;
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /*
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * DMA (thus cache coherency main=
tenance) requires the
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * transfer buffers to live in th=
eir own cache lines.
> > > @@ -231,19 +232,55 @@ static int ad7380_debugfs_reg_access(struct iio=
_dev
> > > *indio_dev, u32 reg,
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return ret;
> > > =C2=A0}
> > >=20
> > > +static int ad7380_buffer_preenable(struct iio_dev *indio_dev)
> > > +{
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 struct ad7380_state *st =3D iio_priv(indio_=
dev);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 struct spi_transfer *xfer;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 int ret;
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 st->msg =3D spi_message_alloc(1, GFP_KERNEL=
);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 if (!st->msg)
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 return -ENOMEM;
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 xfer =3D list_first_entry(&st->msg->transfe=
rs, struct spi_transfer,
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 transfer_list);
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 xfer->bits_per_word =3D st->chip_info->chan=
nels[0].scan_type.realbits;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 xfer->len =3D 4;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 xfer->rx_buf =3D st->scan_data.raw;
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D spi_optimize_message(st->spi, st->m=
sg);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 if (ret) {
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 spi_message_free(st->msg);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 return ret;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 }
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 return 0;
> > > +}
> > > +
> > > +static int ad7380_buffer_postdisable(struct iio_dev *indio_dev)
> > > +{
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 struct ad7380_state *st =3D iio_priv(indio_=
dev);
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 spi_unoptimize_message(st->msg);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 spi_message_free(st->msg);
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 return 0;
> > > +}
> > > +
> >=20
> > Not such a big deal but unless I'm missing something we could have the
> > spi_message (+ the transfer) statically allocated in struct ad7380_stat=
e 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.
> >=20
> > Am I missing something?
>=20
> No, your understanding is correct for the current state of everything
> in this series. So, we could do as you suggest, but I have a feeling
> that future additions to this driver might require that it gets
> changed back this way eventually.

Hmm, not really sure about that as chip_info stuff is always our friend :).=
 And
I'm anyways of the opinion of keeping things simpler and start to evolve wh=
en
really needed (because often we never really need to evolve). But bah, as I
said... this is really not a big deal.

- Nuno S=C3=A1