From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Cameron Subject: Re: [PATCH v2 1/7] iio: adc: max1027: Add debugfs register read support Date: Sat, 12 Oct 2019 14:56:21 +0100 Message-ID: <20191012145621.228d4efc@archlinux> References: <20191003173401.16343-1-miquel.raynal@bootlin.com> <20191003173401.16343-2-miquel.raynal@bootlin.com> <20191006110424.7781d99d@archlinux> <20191007120001.61c8ef71@xps13> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20191007120001.61c8ef71@xps13> Sender: linux-kernel-owner@vger.kernel.org To: Miquel Raynal Cc: Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Rob Herring , Mark Rutland , devicetree@vger.kernel.org, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Petazzoni List-Id: devicetree@vger.kernel.org On Mon, 7 Oct 2019 12:00:01 +0200 Miquel Raynal wrote: > Hi Jonathan, >=20 > Jonathan Cameron wrote on Sun, 6 Oct 2019 11:04:24 > +0100: >=20 > > On Thu, 3 Oct 2019 19:33:55 +0200 > > Miquel Raynal wrote: > > =20 > > > Until now, only write operations were supported. Force two bytes read > > > operation when reading from this register (might be wrong when reading > > > the temperature, but will work with any other value). =20 > >=20 > > That's worrying as comments go. Just return an error on the temperature > > register if it's going to do the wrong thing. =20 >=20 > Actually the debugfs_reg_access hook is supposedly stateless. When > reading registers I don't know what I am reading because the "source" is > selected during the write operation, so I have no reliable way to know > what I am reading. >=20 > I set the read length to 2 bytes because most of the "atomic"reads are > two bytes and it allows us to test various commands directly from > userspace and read meaningful values. This is a limitation as: > * Voltage 'atomic' reads are 2 bytes > * Temperature 'atomic' reads are 2 bytes but never come alone (usually > one voltage input of 2B will follow). > * Any other 'condensed' input will be more than 2 bytes, ie. several > voltage values in one go. >=20 > In any case, doing a software reset of the chip will turn it back > into a working state no matter what was requested/read. >=20 > For me, 2-byte reads is a "good enough" solution that will work with > almost all the simplest ('atomic') SPI operations, but if you think > limiting to 2-bytes access is a problem (right now there is only write > access, which is kind of useless on its own) then let's drop the patch. > But I wanted to contribute it because it really helped me during the > development.=20 This is fine as is. Comment was worrying so could perhaps have given more detail. Still it's a debug interface, people get to look at the datasheet if they are using this :) Jonathan >=20 >=20 > Thanks, > Miqu=C3=A8l