On Mon, Sep 23, 2013 at 10:12 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: > On 09/23/2013 01:53 PM, Linus Walleij wrote: >> I think the kernel should prevent such things. > > It might be nice if it could do that. > > However, that is 100% unrelated to the problem at hand. I don't think it is unrelated when the old OMAP boardfile-based code definately prevents such uses by its strict usage of gpio_request() for all IRQ-bound GPIOs. I think not preventing it for the DT boot path is setting lower standards for DT code than for boardfile code which is not what we should be doing. > A driver which only cares about an IRQ should be able to call just IRQ > APIs and have the HW work. Since not all IRQs are GPIOs, the thing that > causes the HW to work should not involve the GPIO subsystem in any way > at all. Yes I have bought into that concept now. > Having the kernel detect when two different drivers both request the > same resource is entirely another thing. The solution to the first issue > must not rely on any solution to this second issue. I understand this stance from a DT point of view - which is about resource passing and its syntax and semantics. >From a GPIO subsystem point of view, in keeping resources under kernel control, I naturally do not agree. > I'm also not convinced it's possible to solve this second issue given > the current kernel APIs, since there's not enough semantic information; > requests of GPIOs and IRQs aren't actually tied to a particular driver > at present (there's no "struct device *dev" parameter to request_irq or > gpio_request) and so the subsystems can't actually tell who is > requesting the GPIO/IRQ, and hence can't detect when the same driver, or > a different driver, is requesting the same core resource for different > purposes. Solving the issue that e.g. two different drivers competing about the same resource (as in one driver requesting an IRQ and another one requesting a GPIO) is not what I'm after here. I'm more after the GPIO subsystem having knowledge of a certain GPIO line being requested for IRQ, and denying that line to be set as input. Maybe this can actually be achieved quite easily with an additional API? Like gpio_lock_as_irq(gpio) which flags this in .flags of struct gpio_desc and prevent such things? Alexandre what do you think about this idea? > Equally, I am actually not 100% sure we want the core to prevent this. > Why shouldn't two different drivers request the same IRQ? Why shouldn't > at least one driver, perhaps more, request the pin as a GPIO (assuming > it will only read the GPIO value, not flip the pin to output). But I have already stated that this is OK? Are we talking past each other now? > This > exact situation might happen on some Tegra boards where there's a GPIO > for VBUS_EN that affects 2 USB ports. It's supposed to be driven > open-collector. If an external entity forces it low, it means > over-current. You are describing a very good reason for the core to be doing exactly what I described I think? Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
