Re: GPIO static allocation warning with v6.2-rcX

[Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>]

Hi Rob,

Am Montag, 30. Januar 2023, 16:45:57 CET schrieb Rob Herring:
> On Mon, Jan 30, 2023 at 9:02 AM Linus Walleij <linus.walleij@xxxxxxxxxx> 
wrote:
> > On Mon, Jan 30, 2023 at 12:02 PM Marco Felsch <m.felsch@xxxxxxxxxxxxxx> 
wrote:
> > > On 23-01-30, Linus Walleij wrote:
> > > > On Sun, Jan 29, 2023 at 7:33 PM Robert Schwebel
> > > > 
> > > > <r.schwebel@xxxxxxxxxxxxxx> wrote:
> > > > > While this could also be done with a daemon offering a dbus api,
> > > > > this
> > > > > would be significantly more complex. In a critical environment, one
> > > > > needs to make sure that the daemon process never fails, otherwhise
> > > > > the
> > > > > power of the DuT would maybe be in a random state. Then of course
> > > > > one
> > > > > can add a watchdog, but with the current sysfs interface it's really
> > > > > simple. Of course that would also work if the new interface would
> > > > > offer
> > > > > a "keep this line as it is" feature, but adding a dbus daemon just
> > > > > for
> > > > > keeping the state of a pin sounds overcomplex when the kernel could
> > > > > also
> > > > > provide that functionality.
> > > > 
> > > > One issue we face as developers is scaleability. Things that
> > > > seem straight forward on a single board computer in a lab get
> > > > really complex in a big system with man GPIO chips.
> > > > 
> > > > One of the big dangers of the sysfs ABI is that it is dependent on
> > > > probe order which the kernel sadly does not really guarantee.
> > > 
> > > Does it? At least the drive I listed (e.g. the imx gpio driver) uses
> > > aliases to make it reliable.
> > 
> > I'm not sure that is the intended use of the aliases in device tree.
> > (Rob can maybe answer this.)
> 
> The kernel community's position on stable device numbers for userspace
> is quite clear.

Sorry for this stupid question: What position is it? Is it documented 
somewhere?

> That is how aliases get used by the kernel though. IMO, they should be
> limited to a documented set of alias names, and GPIO is not one of
> them. We replaced the whole GPIO sysfs API for this reason (among
> others).

So in which case, or under which circumstances, aliases are acceptable?

Best regards,
Alexander

> IIRC, i.MX is one of the worst abusers with aliases for everything,
> most of which should be removed.
> 
> Rob