From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH 2/2] Make non-linear GPIO ranges accesible from gpiolib Date: Tue, 25 Jun 2013 09:22:02 -0600 Message-ID: <51C9B59A.6000407@wwwdotorg.org> References: <1371128132-18266-2-git-send-email-christian.ruppert@abilis.com> <51BA3BC1.3090109@wwwdotorg.org> <20130614091241.GA23745@ab42.lan> <51C1F42E.5090107@wwwdotorg.org> <51C1F82C.4020502@wwwdotorg.org> <20130620115710.GB942@ab42.lan> <51C4C2ED.5090505@wwwdotorg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Linus Walleij Cc: Christian Ruppert , Patrice CHOTARD , "linux-kernel@vger.kernel.org" , Grant Likely , Rob Herring , Rob Landley , Sascha Leuenberger , Pierrick Hascoet , "devicetree-discuss@lists.ozlabs.org" , "linux-doc@vger.kernel.org" , Alexandre Courbot List-Id: devicetree@vger.kernel.org On 06/25/2013 08:32 AM, Linus Walleij wrote: > On Fri, Jun 21, 2013 at 11:17 PM, Stephen Warren wrote: >> On 06/20/2013 05:57 AM, Christian Ruppert wrote: > >> The Linux pinctrl subsystem specifically doesn't provide mutual >> exclusion between "mux function" and GPIO usage within a pin group, >> although perhaps a driver could internally. > > It used to block this at one point. But it doesn't make sense > when the hardware looks like so: > >>> +- SPI >>> Physical pins --- GPIO --- pinctrl -+- I2C >>> +- mmc > > As in this case it is perfectly legal to enable the GPIO as > input while the I2C bus is running and "spy" on the signals. > > The driver should probably not allow the GPIO output to be > driven while some peripheral is muxed in though, that could be > disastrous... Well, in the HW diagram above, GPIO output probably simply overrides "mux function" output, so everything would work as requested. Whether it makes sense to request such an override is a policy question that pinctrl itself probably shouldn't decide. After all, what if there's a pin group containing 4 pins, which are used by the board as 2 GPIO and 2 I2C. pinctrl shouldn't disallow selecting GPIO on any pin in that pin group simply because I2C is selected on it; that fact doesn't necessarily mean that the selected mux function actually uses every single pin in the group.