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

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Date:	Wed, 13 Aug 2014 15:09:18 +0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Johan Hovold <johan@...nel.org>
Cc:	Hannes Petermaier <Hannes.Petermaier@...automation.com>,
	andi@...as.de, dforsi@...il.com, gnomes@...rguk.ukuu.org.uk,
	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

On Wed, Aug 13, 2014 at 09:05:09AM +0200, Johan Hovold wrote:
> 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.

For some reason I thought I saw some patches recently that was trying to
resolve this problem.  So it might get fixed for 3.18...

thanks,

greg k-h
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