Re: [PATCH v7] usb:serial:pl2303: add GPIOs interface on PL2303

[Johan Hovold <johan@kernel.org>]

On Wed, Aug 13, 2014 at 08:17:50AM +0200, Hannes Petermaier wrote:
> > > 
> > > Known issue:
> > > If gpios are in use(export to userspace through sysfs interface, etc),
> > > then call pl2303_release(unplug usb-serial convertor, modprobe -r, 
> etc),
> > > will cause trouble, so we need to make sure there is no gpio user 
> before
> > > call pl2303_release.
> > 
> > This is a real problem that we need to address. gpiolib isn't really
> > able to handle devices that just disappear. In fact, it's API claims 
> that
> > we must not call gpiochip_remove with requested gpios and this is
> > exactly what you might do in pl2303hx_gpio_release below.
> > 
> > As I mentioned earlier, this crashes the kernel when a new gpiochip is
> > later added (the gpiochip data structures are likely corrupted and we
> > get a NULL pointer deref in gpiochip_find_base).
> > 
> > Linus, any thoughts on this?
> 
> Hi,
> there are several USB to I2C bus adapters and I2C IO-Expanders,
> how is this handled there ?

The short answer is: it isn't.

A few i2c-gpio-expander drivers have teardown callbacks that can be used
from board files to release any gpios requested there, but this neither
translates to device tree or is of any help when gpios have been
exported to user space.

Thanks,
Johan