On Tue, 15 Nov 2022 15:49:46 +0100 Nuno Sá <noname.nuno@xxxxxxxxx> wrote: > On Mon, 2022-11-14 at 19:44 +0000, Jonathan Cameron wrote: > > On Mon, 14 Nov 2022 13:52:26 +0000 > > "Tanislav, Cosmin" <Cosmin.Tanislav@xxxxxxxxxx> wrote: > > > > > > -----Original Message----- > > > > From: Jonathan Cameron <jic23@xxxxxxxxxx> > > > > Sent: Saturday, November 12, 2022 7:07 PM > > > > To: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> > > > > Cc: Tanislav, Cosmin <Cosmin.Tanislav@xxxxxxxxxx>; Lars-Peter > > > > Clausen > > > > <lars@xxxxxxxxxx>; Hennerich, Michael > > > > <Michael.Hennerich@xxxxxxxxxx>; > > > > devicetree@xxxxxxxxxxxxxxx; Rob Herring <robh+dt@xxxxxxxxxx>; > > > > linux- > > > > iio@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > > > > Subject: Re: [PATCH 5/5] iio: addac: ad74413r: add support for > > > > reset-gpio > > > > > > > > [External] > > > > > > > > On Fri, 11 Nov 2022 15:39:21 +0100 > > > > Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > We have a board where the reset pin of the ad74412 is connected > > > > > to a > > > > > gpio, but also pulled low by default. Hence to get the chip out > > > > > of > > > > > reset, the driver needs to know about that gpio and set it high > > > > > before > > > > > attempting to communicate with it. > > > > > > > > I'm a little confused on polarity here. The pin is a !reset so > > > > we need to drive it low briefly to trigger a reset. > > > > I'm guessing for your board the pin is set to active low? (an > > > > example > > > > in the dt would have made that clearer) Hence the pulse > > > > in here to 1 is actually briefly driving it low before restoring > > > > to high? > > > > > > > > For a pin documented as !reset that seems backwards though you > > > > have > > > > called it reset so that is fine, but this description doesn't > > > > make that > > > > celar. > > > > > > My opinion is that the driver shouldn't exactly know the polarity > > > of the reset, > > > and just assume that setting the reset GPIO to 1 means putting it > > > in reset, > > > and setting it to 0 means bringing out of reset. > > > > Agreed. I'd just like a comment + example in the dt-binding to make > > the point > > that the pin is !reset. > > > > Preferably with an example in the dt binding of the common case of it > > being wired > > up to an active low pin. > > > > The main oddity here is the need to pulse it rather than request it > > directly as > > in the reset state and then just set that to off. > > > > > > Agreed... In theory we should be able to request the gpio with > GPIOD_OUT_HIGH and then just bring the device out of reset If I recall correctly the datasheet specifically calls out that a pulse should be used. No idea if that's actually true, or if it was meant to be there just to say it needs to be set for X nsecs. Jonathan > > - Nuno Sá >
