From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [PATCH 2/2] i2c-dev: Don't block the adapter from unregistering Date: Wed, 6 Jul 2016 07:33:23 -0700 Message-ID: <20160706143323.GK2671@ubuntu> References: <021486be2f5425ce2379219a7ac163ee14ba2aba.1467772840.git.viresh.kumar@linaro.org> <415dcaa7-8ad9-492e-5c5c-605173bc4345@axentia.se> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pf0-f177.google.com ([209.85.192.177]:35755 "EHLO mail-pf0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753130AbcGFOd0 (ORCPT ); Wed, 6 Jul 2016 10:33:26 -0400 Received: by mail-pf0-f177.google.com with SMTP id c2so80459714pfa.2 for ; Wed, 06 Jul 2016 07:33:26 -0700 (PDT) Content-Disposition: inline In-Reply-To: <415dcaa7-8ad9-492e-5c5c-605173bc4345@axentia.se> Sender: linux-i2c-owner@vger.kernel.org List-Id: linux-i2c@vger.kernel.org To: Peter Rosin Cc: Wolfram Sang , Jean Delvare , linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, Johan Hovold , Alex Elder On 06-07-16, 10:22, Peter Rosin wrote: > On 2016-07-06 04:57, Viresh Kumar wrote: > > The i2c-dev calls i2c_get_adapter() from the .open() callback, which > > doesn't let the adapter device unregister unless the .close() callback > > is called. > > > > On some platforms (like Google ARA), this doesn't let the modules > > (hardware attached to the phone) eject from the phone as the cleanup > > path for the module hasn't finished yet (i2c adapter not removed). > > > > We can't let the userspace block the kernel forever in such cases. > > > > Fix this by calling i2c_get_adapter() from all other file operations, > > i.e. read/write/ioctl, to make sure the adapter doesn't get away while > > we are in the middle of a operation, but not otherwise. In .open() we > > will release the adapter device before returning and so if there is no > > data transfer in progress, then the i2c-dev doesn't block the adapter > > from unregistering. > > > > Signed-off-by: Viresh Kumar > > --- > > drivers/i2c/i2c-dev.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++----- > > include/linux/i2c.h | 1 + > > 2 files changed, 66 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c > > index 66f323fd3982..b2562603daa9 100644 > > --- a/drivers/i2c/i2c-dev.c > > +++ b/drivers/i2c/i2c-dev.c > > @@ -142,13 +142,25 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count, > > int ret; > > > > struct i2c_client *client = file->private_data; > > + struct i2c_adapter *adap; > > + > > + adap = i2c_get_adapter(client->adapter_nr); > > + if (!adap) > > + return -ENODEV; > > + > > + if (adap != client->adapter) { > > + ret = -EINVAL; > > + goto put_adapter; > > + } > > I don't see how this can work with the i2c-demux-pinctrl driver. > I also wonder if/how other muxes handle this relaxed adapter > lifetime thingy? I would like to mention here that I am no I2C expert and have limited knowledge of it :) I haven't had a look at the muxes implementation earlier, now that I looked at them, I see that they unregister/register the adapter, perhaps while switching functionality. I am not sure though, if this patch will break it or not. And I don't have a way of testing it out. > Out of curiosity, why would client->adapter change anyway? > (that is, if not because of a demux-pinctrl op) I didn't mean that it will change, and perhaps we can add a WARN_ON(adap != client->adapter). But, thinking about it again now, I think it is possible. What about this sequence: - i2c-adap-register (address P1) - .open(), client->adapter = P1; - .read/write/ioctl().. - i2c-adap-unregister (adapter freed) - i2c-adap-register with same adapter_nr (address P2); - .read/write/ioctl(). Wouldn't the address differ here ? -- viresh