On 12/03/2013 02:29 AM, Linus Walleij wrote: ... > So I guess what you're after is a kind of hog that will be pushed > aside and ignored if a struct device with an associated state appears > that will use the same pin? That probably would be useful. Perhaps we should just make all hogs not exclusively own the pins they configure? > It is true that we currently require the tables to be strict and not > overlap like this, so ideally you should remove the hogs when you > have a device driver, but you're actually describing an interesting > case here: > > What if I have a driver for this IP block, and it was supposed to > take care of a few pins, but I decide not to compile it into my > kernel? Or if I have it as a module and only modprobe it later > at runtime? Indeed, that's the nasty hole in pushing even static per-device pinctrl configuration into each device's node; the device may not appear. Related, I prefer to put /all/ static pinctrl configuration into the pinctrl device's "default" state (i.e. use a hog) rather than configuring the static pinctrl setup per device, for another reason too: If a particular IO controller's signals can be routed to n different (sets of) pins, then we need to do *both* of the following when setting up the pinmux: a) Configure the pins we want to host those signals to route to/from that particular IO controller. b) Configure any other pins that could route to/from that particular IO controller as some other function; either disabled, or routed to/from some different IO controller. That is so that the IO controller's RX/input signals are not connected from two different sets of pins at once, which would cause two things to driver them. Depending on HW, this could cause on of: 1) Multiple drivers -> high power usage, or even Silicon damage. 2) Inconsistent configuration, with the "wrong" set of pins driving the IO controller's inputs, and hence the signals on the "correct" pins being ignored -> hard to find bug. Now, (a) could easily happen when the driver for the IO controller is probed. However, (b) can't, because some other IO controller may need to use those pins, and the two drivers (or pinctrl states for different devices) can't both set up those pins. The only way to solve this is to set up all pinmux state using a single global table (e.g. the pin controller's default state, or hog) that is applied early on. If we rely on resolving these conflicts in per-device default/... states, then that means the conflicts won't get resolved until a driver gets probed, if it ever does, which is too late. ... and as such, I prefer only putting *dynamic* configuration into per-device (non-hog) nodes. (e.g. an I2C bus mux driver which actively changes the pinmux at run-time to move an I2C controller between different sets of SoC pins). -- 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
