On Wed, Jan 10, 2018 at 1:37 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > On Wed, Jan 10, 2018 at 2:58 AM, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote: > >> Some qcom platforms make some GPIOs or pins unavailable for use >> by non-secure operating systems, and thus reading or writing the >> registers for those pins will cause access control issues. >> Introduce a DT property to describe the set of GPIOs that are >> available for use so that higher level OSes are able to know what >> pins to avoid reading/writing. What level of access control is implemented here? Is there access control for each GPIO individually, or is it done by banks of GPIOs? Just asking to make sure I understand the problem domain. >> >> Cc: <devicetree@xxxxxxxxxxxxxxx> >> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx> > > I like the idea, let's check what we think about the details regarding > naming and semantics, I need feedback from some DT people > in particular. > > Paging in Grant on this as he might have some input. > >> I stuck this inside msm8996, but maybe it can go somewhere more generic? > > Yeah just put it in Documentation/devicetree/bindings/gpio/gpio.txt > Everyone and its dog doing GPIO reservations "from another world" > will need to use this. > >> +- ngpios-ranges: >> + Usage: optional >> + Value type: <prop-encoded-array> >> + Definition: Tuples of GPIO ranges (base, size) indicating >> + GPIOs available for use. >> + >> Please refer to ../gpio/gpio.txt and ../interrupt-controller/interrupts.txt for >> a general description of GPIO and interrupt bindings. > > I like the tuples syntax. That's fine. It's like gpio-ranges we have > already to map between pin controllers and GPIO. > > I don't think we can reuse gpio-ranges because that is > exclusively for pin control ATM, it would be fine if the ranges > were for a specific device, like pin control does, like: > > gpio-ranges = <&secure_world_thing 0 20 10>; > > But you definately would need a node to tie it to, so that the > driver for that node can specify that it's gonna take the > GPIOs. > > But I think the semantics should be the inverse. That you > point out "holes" with the lines we *can't* use. > > We already support a generic property "ngpios" that says how > many of the GPIOs (counted from zero) that can be used, > so if those should be able to use this as a generic property it > is better with the inverse semantics and say that the > "reserved-gpio-ranges", "secureworld-gpio-ranges" > (or whatever we decide to call it) takes precedence over > ngpios so we don't end up in ambigous places. Heh, I just went down the same thought process on the naming before I read the above. Yes I agree. The property name should have something like "reserved" in it. I vote for "gpio-reserved-ranges" because it puts the binding owner (gpio) at the front of the name, it indicates that the list is unavailable GPIOs, and that the format is a set of ranges. The fiddly bit is it assumes the GPIOs are described by a single number. It works fine as long as the GPIO controllers can use a single cell to describe a gpio number (instead of having #gpio-cells = 3 with the first cell being bank, the second being number in bank, and the third being flags). > > Then, will it be possible to put the parsing, handling and > disablement of these ranges into drivers/gpio/gpiolib-of.c > where we handle the ranges today, or do we need to > do it in the individual drivers? I certainly would prefer parsing this in common code, and not in individual drivers, but again it becomes hard for any driver using multiple cells to describe the local GPIO number. I think the guidance here needs to be that the property is relevant when the internal GPIO number representation fits within a uint32, which realistically should never be a problem. g. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
