From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <5b9f3f64.1c69fb81.6cb6.b5ef@mx.google.com> From: Rob Herring Subject: Re: [PATCH 2/2] dt-bindings: gpio: Add binding for gpio-mockup References: <20180905132618.31274-1-vincent.whitchurch@axis.com> <20180905132618.31274-2-vincent.whitchurch@axis.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Date: Sun, 16 Sep 2018 18:24:52 -0500 To: Linus Walleij Cc: Bartosz Golaszewski , vincent.whitchurch@axis.com, "open list:GPIO SUBSYSTEM" , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Rabin Vincent List-ID: On Thu, Sep 06, 2018 at 02:47:23PM +0200, Linus Walleij wrote: > On Thu, Sep 6, 2018 at 1:09 PM Bartosz Golaszewski wrote: > > > Do we even need DT bindings for this? Device tree bindings mean that > > we commit to a stable interface so that once a device with given DT > > blob is released, it will work on every future kernel. Also: DT should > > only include information about actual HW, not operating system > > concepts. Meanwhile this is for testing purposes only and it won't end > > up in any actual DT source file upstream. > > Hm that relates to another discussion I have with the DT maintainers > about a virtualized display panel. > > I do not know how the DT maintainers feel about supporting things > in the kernel that uses DT infrastructure and specially tailored > device trees but include elements with no formal device tree > bindings. Would be interesting to hear their thoughts on this. I have one usecase in mind where I think it is valid, but for this case in particular, I think it would be better to just provide a sysfs interface. If there's no GPIO binding connections to this mockup controller, there's no real need for DT. OTOH, if this device allowed building a test framework for all the other GPIO based drivers and bindings such as LED, PWM, bitbanged buses, etc. The case I have in mind is where you want to attach a fake DT node to a non-DT device for the purposes of defining other downstream devices. For example, an FTDI USB to serial chip with downstream SPI, UART, I2C, GPIO, etc. devices attached. This could be on an x86 which doesn't have a base DT. Rob