lkml.org 
[lkml]   [2015]   [Jan]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v5 1/3] gpio: Cygnus: define Broadcom Cygnus GPIO binding
    On Tue, Jan 13, 2015 at 09:06:15AM +0100, Linus Walleij wrote:
    > On Wed, Dec 17, 2014 at 11:44 AM, Russell King - ARM Linux
    > <linux@arm.linux.org.uk> wrote:
    > > On Wed, Dec 17, 2014 at 11:45:01AM +0900, Alexandre Courbot wrote:
    > >> Actually we are not that far from being able to do completely without
    > >> any GPIO number, and maybe that's what we should aim for. I think the
    > >> only remaining offender is the sysfs interface.
    > >
    > > And that is a user API, and there's lots of users of it (eg, on Raspberry
    > > Pi platforms.) So changing it isn't going to be easy - I'd say that it's
    > > impractical.
    > >
    > > What you're suggesting would be like re-numbering Linux syscalls.
    >
    > The problem is that right now if we set the .base of a gpio_chip
    > to -1 for dynamic allocation of GPIO numbers and we have more
    > than one GPIO chip in the system, the numbers basically depend
    > on probe order, and may theoretically even differ between two boots.
    >
    > So in these cases preserving the ABI means preserving the
    > unpredictability of these assigned numbers or something.
    >
    > For the old usecases with a single GPIO controller and a fixed
    > base offset of e.g. 0 (which I suspect was implicit in the initial
    > design of the subsystem) things work fine as always, it's these new
    > dynamic use cases that destabilize the ABI.

    Since GPIOs are exported through sysfs into userland by GPIO number,
    and we know that there are users of it (see
    https://github.com/pilight/wiringX) which hard encode GPIO numbers,
    so this is *really* something that we as kernel developers can't
    change without breaking such users.

    So, what I'm saying is be very careful about moving to a fully
    dynamic space: you could end up breaking userspace if you do.

    --
    FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
    according to speedtest.net.


    \
     
     \ /
      Last update: 2015-01-13 13:21    [W:2.509 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site