Re: Userspace and Device-Tree

[Alexandre Courbot <gnurou-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Tue, Sep 1, 2015 at 4:20 AM, Chris Read <chrisrfq-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> From what I see the standard kernel allows exposing GPIOs to userspace.
> There are kernel calls to do so.  It seems to be recognized as an important
> feature.  The standard kernel also has a regulator-consumer whose whole
> purpose is to expose control of a regulator to userspace.  So it looks like
> such userspace control is intended.
>
> My concern is that, while these features are appropriate to expose in
> userspace, I can't expose them using what are now the standard ways
> (i.e. without a board file or customized driver for each board).  I'd like
> to have a way to use the same kernel for all our boards, and have a
> configuration that can be provided that will expose the required ones.
>
> It may be possible to make it a set of kernel command line parameters,
> which would then be customized for each board.  There are, no doubt,
> still other ways to accomplish this board-specific customization.
> However, since there is already a board-specific mechanism to do
> kernel driver/module configuration (i.e. DT), it seemed like a good idea
> to piggy-back on it.
>
> Obviously exporting to userspace isn't a hardware configuration
> parameter, but the mechanism of hooking up and configuring drivers
> that DT uses looks to me like the most efficient way implement this.

Since the GPIO sysfs allows you to request any GPIO that is not
claimed by a kernel driver from userspace, is there a reason why you
cannot simply run board-specific init scripts that request and
configure the GPIOs you need? Once GPIO naming is merged, this should
be as elegant as it gets for what you want to do.
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