From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mika Westerberg Subject: Re: [PATCH] pinctrl: baytrail: show output gpio state correctly on Intel Baytrail Date: Mon, 3 Nov 2014 20:42:47 +0200 Message-ID: <20141103184247.GD1618@lahna.fi.intel.com> References: <20141028144249.GD8123@saruman> <20141031132005.GB1273@saruman> <20141031162339.GA7136@psi-dev26.jf.intel.com> <20141031184509.GA2224@psi-dev26.jf.intel.com> <20141103092402.GA1304@lahna.fi.intel.com> <20141103150048.GB27425@saruman> <20141103152743.GB1618@lahna.fi.intel.com> <20141103154207.GC1618@lahna.fi.intel.com> <20141103155011.GH27425@saruman> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20141103155011.GH27425@saruman> Sender: stable-owner@vger.kernel.org To: Felipe Balbi Cc: David Cohen , Linus Walleij , "linux-kernel@vger.kernel.org" , "linux-gpio@vger.kernel.org" , stable , mathias.nyman@linux.intel.com List-Id: linux-gpio@vger.kernel.org On Mon, Nov 03, 2014 at 09:50:11AM -0600, Felipe Balbi wrote: > Hi, > > On Mon, Nov 03, 2014 at 05:42:07PM +0200, Mika Westerberg wrote: > > On Mon, Nov 03, 2014 at 05:27:43PM +0200, Mika Westerberg wrote: > > > On Mon, Nov 03, 2014 at 09:00:48AM -0600, Felipe Balbi wrote: > > > > On Mon, Nov 03, 2014 at 11:24:02AM +0200, Mika Westerberg wrote: > > > > > On Fri, Oct 31, 2014 at 11:45:09AM -0700, David Cohen wrote: > > > > > > > I think adding the module exit + allowing this driver to be a module > > > > > > > would be a good approach. Then we don't need to force generic x86 kernel > > > > > > > binaries to always have this driver. Unless Mathias or Mika knows a > > > > > > > constraint to force this driver to be builtin only. > > > > > > > > > > > > It helps if I CC them when asking for feedback :) > > > > > > > > > > > > Mathias, Mika, do you know any constraint that forces pinctrl-baytrail > > > > > > to be bool? > > > > > > > > > > The only constraint that has been keeping this driver as bool is that > > > > > some machines like, Asus T100, uses ACPI GPIO operation regions for > > > > > toggling GPIOs to get things like sensor hub powered on. The GPIO > > > > > operation region code does not yet handle -EPROBE_DEFER so only way to > > > > > ensure that the operation region is there is to have the driver compiled > > > > > in to the kernel. > > > > > > > > But that's not enough excuse to have every single x86 in the market > > > > shipping with this driver. Think about a distro kernel, most likely this > > > > gets enabled and it's wrong in 80% of the cases. > > > > > > True, but see below. > > > > > > > It would be nicer to add EPROBE_DEFER support, convert this into > > > > tristate and have default = M if BAYTRAIL, or something. > > > > > > If it were simple as that we would have done that already. Please check > > > drivers/gpio/gpiolib-acpi.c:acpi_gpio_adr_space_handler() and tell me > > > how we can do that. > > > > Actually the above is not the problem because we already have registered > > the GPIO chip and hence we have the GPIO available to the firmware code. > > what happens before you registered the gpio chip ? It takes some time > from head.S to gpiochip_irqchip_add(). Anywhere between that time, > firmware could try to access gpios and the same problem would occur. The operation region is not ready and the firmware does not try to use it. However, the subsys_initcall() is there just to be sure that the GPIO driver gets loaded before anything that is going to use GPIOs from firmware. > > The real problem is that if the ACPI GPIO operation handler is not there > > at the time firmware decides to do something it will just skip things > > that depend on the operation region. So if it has a GPIO that is used to > > turn on sensor hub or touch panel or whatever, this will not be done and > > it results that the device in question might not work properly. > > that's an issue that needs solving, but forcing every x86 kernel to ship > with this driver, is not a proper solution. I would rather have the driver build in to the kernel now (and btw it has been already in mainline quite some time so I suspect many distros have already enabled it), than turning it module and render some devices that have been working previously, fail suddenly. There is a mechanism in ACPI to solve these issues, called _DEP, but it is still very much work in progress.