Re: Userspace and Device-Tree

[Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Tue, Sep 22, 2015 at 6:54 AM, Chris Read <chrisrfq-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On Mon, Sep 21, 2015 at 4:55 PM, Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
>> On Wed, Sep 2, 2015 at 6:35 AM, Chris Read <chrisrfq-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>> There are some hardware aspects/parameters
>>> of exporting that aren't controllable from userspace, such as whether or not
>>> reversing the direction of a GPIO is safe.
>>
>> The original argument as to why kernel should handle hardware
>> is to keep things safe and under control.
>>
>> I don't understand this argument really, should the kernel give you
>> a gun but stop you from shooting yourself in the foot with it or
>> what do you mean? Then the stance of kernel not to give out guns
>> is better.
>
> From my embedded perspective a board designer wants to keep
> hardware safe and under control too.  He may want or need to expose
> controls or status to userspace applications, though, and what he
> wants to have exposed may vary from board to board.  I just feel that
> exposing them via the DT could be OK, whereas others do not.

I am usually conservative with this because all too often, people
do not know about all the stuff listed in
Documentation/gpio/drivers-on-gpio.txt
and their usual reasoning is "just lemme do this in userspace real
quick now because I have this project". And that doesn't sit well with
our long-term view of kernel ABIs.

For proper userspace ABI the sysfs has been deemed unusable
and does not scale. What is needed is a chardev rewrite as has
been discussed several times.

Yours,
Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html