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

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Date:	Wed, 13 Aug 2014 08:17:50 +0200
From:	Hannes Petermaier <Hannes.Petermaier@...automation.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	andi@...as.de, dforsi@...il.com, gnomes@...rguk.ukuu.org.uk,
	gregkh@...uxfoundation.org, jhovold@...il.com,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-kernel@...r.kernel.org, linux-kernel-owner@...r.kernel.org,
	linux-usb@...r.kernel.org, Wang YanQing <udknight@...il.com>
Subject: Re: [PATCH v7] usb:serial:pl2303: add GPIOs interface on PL2303

> > 
> > 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 ?

Maybe we you can take some idea from there.

best regards,
Hannes


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