Re: [PATCH] gpio: Do not trigger WARN() with sysfs gpio export/unexport

[Damien Le Moal <Damien.LeMoal@xxxxxxx>]

On Tue, 2020-11-10 at 15:40 +0100, Bartosz Golaszewski wrote:
> On Tue, Nov 10, 2020 at 3:31 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> > 
> > On Fri, Nov 6, 2020 at 12:27 PM Damien Le Moal <Damien.LeMoal@xxxxxxx> wrote:
> > 
> > > It may not be the best interface for regular end users to
> > > manipulate gpios, but it is definitely super useful for developers to do quick
> > > tests of their setup/drivers (which is what I did for my work with the Kendryte
> > > K210 RISC-V SoC support).
> > 
> > It is a bit discouraging that RISC-V, which was invented after we already
> > obsoleted the sysfs ABI, is deploying this for development and test.
> > 
> > We need to think about a similar facility for users which is less
> > damaging but fulfils the same needs. I think I saw something a while
> > back that looked promising and added some funky files in debugfs
> > in a hierarchical manner per-gpiochip instead. That is how debugfs
> > should be used.
> > 
> 
> Basically something like what gpio-mockup does for events? Was it
> something out-of-tree or was it on the mailing list?
> 
> Also: quick tests have the tendency to become long-term solutions. :)
> 
> Is gpioget/gpioset duo difficult/cumbersome to use? It's a serious
> question - I wrote it in a way that was as user-friendly as possible
> but maybe I'm missing something about sysfs that makes users prefer it
> over a command-line tool. To me sysfs was always a PITA with the
> global numbers etc. but it still seems to stick with others.

In my particular case, I am using a simple busybox userspace that has nothing
else but a shell, so I did not have the gpioget/gpioset tools. And to be frank,
I did not even know what tool to use to control GPIOs. It is the first time I
am touching GPIOs with Linux and did not spent time to study what should be
used once I saw that sysfs allowed controlling the pins for tests.

Removing sysfs entirely would likely force people to look for these tools to do
tests, and I really am an example here :)

I am using buildroot to generate the toolchain and busybox userspace for the
board.  I now see that libgpiod and gpio tools packages are in there but for
whatever reasons, I cannot select them for my RISC-V build. Will need to
explore why.


-- 
Damien Le Moal
Western Digital