Hi, On Mon, Nov 03, 2014 at 08:42:47PM +0200, Mika Westerberg 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. alright, so how does the firmware know that the operation region is ready and why can't that be deferred until pinctrl-baytrail (module or built-in) has finished probing ? That would sort both issues, would it not ? > > > 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. that's why I said you should default to Y if BAYTRAIL or make it tristate and always default to M. > There is a mechanism in ACPI to solve these issues, called _DEP, but it > is still very much work in progress. alright. -- balbi
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