Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:3 as permitted sender) client-ip=2620:137:e000::3:3;
Date:   Wed, 27 Sep 2023 11:27:41 +0300
From:   Matti Vaittinen <mazziesaccount@gmail.com>
To:     Matti Vaittinen <mazziesaccount@gmail.com>,
        Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Cc:     Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Matti Vaittinen <mazziesaccount@gmail.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Angel Iglesias <ang.iglesiasg@gmail.com>,
        Andreas Klinger <ak@it-klinger.de>,
        Benjamin Bara <bbara93@gmail.com>,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v4 2/5] iio: improve doc for available_scan_mask
Message-ID: <4e43bf0186df5c8a56b470318b4827605f9cad6c.1695727471.git.mazziesaccount@gmail.com>
References: <cover.1695727471.git.mazziesaccount@gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="ysY46l6I9tFYuZdP"
Content-Disposition: inline
In-Reply-To: <cover.1695727471.git.mazziesaccount@gmail.com>
Precedence: bulk


--ysY46l6I9tFYuZdP
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

The available_scan_mask is an array of bitmaps representing the channels
which can be simultaneously enabled by the driver. In many cases, the
hardware can offer more channels than what the user is interested in
obtaining. In such cases, it may be preferred that only a subset of
channels are enabled, and the driver reads only a subset of the channels
=66rom the hardware.

Some devices can't support all channel combinations. For example, the
BM1390 pressure sensor must always read the pressure data in order to
acknowledge the watermark IRQ, while reading temperature can be omitted.
So, the available scan masks would be 'pressure and temperature' and
'pressure only'.

When IIO searches for the scan mask it asks the driver to use, it will
pick the first suitable one from the 'available_scan_mask' array. Hence,
ordering the masks in the array makes a difference. We should 'prefer'
reading just the pressure from the hardware (as it is a cheaper operation
than reading both pressure and temperature) over reading both pressure
and temperature. Hence, we should set the 'only pressure' as the first
scan mask in available_scan_mask array. If we set the 'pressure and
temperature' as first in the array, then the 'only temperature' will never
get used as 'pressure and temperature' can always serve the user's
needs.

Add (minimal) kerneldoc to the 'available_scan_mask' to hint the user
that the ordering of masks matters.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
---
 include/linux/iio/iio.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 202e55b0a28b..7bfa1b9bc8a2 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -556,7 +556,9 @@ struct iio_buffer_setup_ops {
  *			and owner
  * @buffer:		[DRIVER] any buffer present
  * @scan_bytes:		[INTERN] num bytes captured to be fed to buffer demux
- * @available_scan_masks: [DRIVER] optional array of allowed bitmasks
+ * @available_scan_masks: [DRIVER] optional array of allowed bitmasks. Sor=
t the
+ *			   array in order of preference, the most preferred
+ *			   masks first.
  * @masklength:		[INTERN] the length of the mask established from
  *			channels
  * @active_scan_mask:	[INTERN] union of all scan masks requested by buffers
--=20
2.41.0


--=20
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =3D]=20

--ysY46l6I9tFYuZdP
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAEBCAAdFiEEIx+f8wZb28fLKEhTeFA3/03aocUFAmUT530ACgkQeFA3/03a
ocVWFggAzH/J6YyXt2/bFTdC4/7cF9pTBmmxoFHEZ9Gdda0iWn6aXAL0VVjfBqxd
0qjKQGd4iPI0Zhwq1BulAAe6+fkpaFS034VD7vLz8uMj2nGLRGFAiSdh1XV5p9xe
nIf2lFYts605GZvmpbMAbUgoXCjhUHuFlId/Az/brI86vlLhMJnGC/1GIO1tZV++
gCBY3AoycklGLNnFviVCLjt8Gkn2qPgT3ZZc5zadtKFR8rQY5q2hmlrfpdg9RpD7
7ko0xsynsMnv7XRAJxtpKD+mW6Xk/nyLwA3ENqzMjRj9K3+OFlsBm6D+bzH92rBR
GSM3U14IBVeVpFmZPAESzT4olJeAYQ==
=/H1j
-----END PGP SIGNATURE-----

--ysY46l6I9tFYuZdP--