From patchwork Mon Apr 24 14:10:46 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Philipp Zabel X-Patchwork-Id: 754281 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3wBSth6KHZz9sN5 for ; Tue, 25 Apr 2017 00:11:08 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762460AbdDXOLF (ORCPT ); Mon, 24 Apr 2017 10:11:05 -0400 Received: from metis.ext.4.pengutronix.de ([92.198.50.35]:47987 "EHLO metis.ext.4.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1172163AbdDXOLE (ORCPT ); Mon, 24 Apr 2017 10:11:04 -0400 Received: from lupine.hi.pengutronix.de ([2001:67c:670:100:3ad5:47ff:feaf:1a17] helo=lupine) by metis.ext.pengutronix.de with esmtp (Exim 4.84_2) (envelope-from ) id 1d2ehW-000413-Ds; Mon, 24 Apr 2017 16:10:50 +0200 Message-ID: <1493043046.2446.37.camel@pengutronix.de> Subject: Re: [PATCH v14 00/11] mux controller abstraction and iio/i2c muxes From: Philipp Zabel To: Peter Rosin Cc: Jonathan Cameron , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Wolfram Sang , Rob Herring , Mark Rutland , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Jonathan Corbet , linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, linux-iio@vger.kernel.org, linux-doc@vger.kernel.org, Andrew Morton , Colin Ian King , Paul Gortmaker , kernel@pengutronix.de Date: Mon, 24 Apr 2017 16:10:46 +0200 In-Reply-To: <2d978956-d247-917d-4150-a6723917a733@axentia.se> References: <1493022995-16917-1-git-send-email-peda@axentia.se> <1493031179.2446.9.camel@pengutronix.de> <2d978956-d247-917d-4150-a6723917a733@axentia.se> X-Mailer: Evolution 3.12.9-1+b1 Mime-Version: 1.0 X-SA-Exim-Connect-IP: 2001:67c:670:100:3ad5:47ff:feaf:1a17 X-SA-Exim-Mail-From: p.zabel@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-i2c@vger.kernel.org Sender: linux-i2c-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org On Mon, 2017-04-24 at 13:37 +0200, Peter Rosin wrote: > On 2017-04-24 12:52, Philipp Zabel wrote: > > On Mon, 2017-04-24 at 10:36 +0200, Peter Rosin wrote: > >> Hi! > >> > >> The big change since v13 is that the mux state is now locked with a mutex > >> instead of an rwsem. Other that that, it is mostly restructuring and doc > >> changes. There are a few other "real" changes as well, but those changes > >> feel kind of minor. I guess what I'm trying to say is that although the > >> list of changes for v14 is longish, it's still basically the same as last > >> time. > > > > I have hooked this up to the video-multiplexer and now I trigger > > the lockdep debug_check_no_locks_held error message when selecting the > > mux input from userspace: > > > > $ media-ctl --links "'imx6-mipi-csi2':1->'ipu1_csi0_mux':0[1]" > > [ 66.258368] > > [ 66.259919] ===================================== > > [ 66.265369] [ BUG: media-ctl/258 still has locks held! ] > > [ 66.270810] 4.11.0-rc8-20170424-1+ #1305 Not tainted > > [ 66.275863] ------------------------------------- > > [ 66.282158] 1 lock held by media-ctl/258: > > [ 66.286464] #0: (&mux->lock){+.+.+.}, at: [<8074a6c0>] mux_control_select+0x24/0x50 > > [ 66.294424] > > [ 66.294424] stack backtrace: > > [ 66.298980] CPU: 0 PID: 258 Comm: media-ctl Not tainted 4.11.0-rc8+ #1305 > > [ 66.306771] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) > > [ 66.313334] Backtrace: > > [ 66.315858] [<8010e5a4>] (dump_backtrace) from [<8010e8ac>] (show_stack+0x20/0x24) > > [ 66.323473] r7:80e518d0 r6:80e518d0 r5:600d0013 r4:00000000 > > [ 66.329190] [<8010e88c>] (show_stack) from [<80496cf4>] (dump_stack+0xb0/0xdc) > > [ 66.336470] [<80496c44>] (dump_stack) from [<8017e404>] (debug_check_no_locks_held+0xb8/0xbc) > > [ 66.345043] r9:ae8566b8 r8:ad88dc84 r7:ad88df58 r6:ad88dc84 r5:ad88df58 r4:ae856400 > > [ 66.352837] [<8017e34c>] (debug_check_no_locks_held) from [<8012b258>] (do_exit+0x79c/0xcc8) > > [ 66.361321] [<8012aabc>] (do_exit) from [<8012d25c>] (do_group_exit+0x4c/0xcc) > > [ 66.368581] r7:000000f8 > > [ 66.371161] [<8012d210>] (do_group_exit) from [<8012d2fc>] (__wake_up_parent+0x0/0x30) > > [ 66.379120] r7:000000f8 r6:76f71798 r5:00000000 r4:00000001 > > [ 66.384837] [<8012d2dc>] (SyS_exit_group) from [<80109380>] (ret_fast_syscall+0x0/0x1c) > > > > That correctly warns that the media-ctl process caused the mux->lock to > > be locked and still held when the process exited. Do we need a usage > > counter based mechanism for muxes that are (indirectly) controlled from > > userspace? [...] > The question then becomes how to best tell the mux core that you want > an exclusive mux. I see two options. Either you declare a mux controller > as exclusive up front somehow (in the device tree presumably), or you > add a mux_control_get_exclusive call that makes further calls to > mux_control_get{,_exclusive} fail with -EBUSY. I think I like the > latter better, if that can be made to work... How about an atomic use_count on the mux_control, a bool shared that is only set by the first consumer, and controls whether selecting locks? ----------8<---------- ---------->8---------- regards Philipp --- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/drivers/mux/mux-core.c b/drivers/mux/mux-core.c index c02fa4dd2d099..1d18bb7f15e07 100644 --- a/drivers/mux/mux-core.c +++ b/drivers/mux/mux-core.c @@ -372,11 +372,12 @@ int mux_control_select(struct mux_control *mux, unsigned int state) { int ret; - mutex_lock(&mux->lock); + if (mux->shared) + mutex_lock(&mux->lock); ret = __mux_control_select(mux, state); - if (ret < 0) + if (ret < 0 && mux->shared) mutex_unlock(&mux->lock); return ret; @@ -399,12 +400,12 @@ int mux_control_try_select(struct mux_control *mux, unsigned int state) { int ret; - if (!mutex_trylock(&mux->lock)) + if (mux->shared && !mutex_trylock(&mux->lock)) return -EBUSY; ret = __mux_control_select(mux, state); - if (ret < 0) + if (ret < 0 && mux->shared) mutex_unlock(&mux->lock); return ret; @@ -427,7 +428,8 @@ int mux_control_deselect(struct mux_control *mux) mux->idle_state != mux->cached_state) ret = mux_control_set(mux, mux->idle_state); - mutex_unlock(&mux->lock); + if (mux->shared) + mutex_unlock(&mux->lock); return ret; } @@ -447,18 +449,13 @@ static struct mux_chip *of_find_mux_chip_by_node(struct device_node *np) return dev ? to_mux_chip(dev) : NULL; } -/** - * mux_control_get() - Get the mux-control for a device. - * @dev: The device that needs a mux-control. - * @mux_name: The name identifying the mux-control. - * - * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno. - */ -struct mux_control *mux_control_get(struct device *dev, const char *mux_name) +static struct mux_control *__mux_control_get(struct device *dev, + const char *mux_name, bool shared) { struct device_node *np = dev->of_node; struct of_phandle_args args; struct mux_chip *mux_chip; + struct mux_control *mux; unsigned int controller; int index = 0; int ret; @@ -505,9 +502,56 @@ struct mux_control *mux_control_get(struct device *dev, const char *mux_name) } get_device(&mux_chip->dev); - return &mux_chip->mux[controller]; + + mux = &mux_chip->mux[controller]; + + ret = atomic_inc_return(&mux->use_count); + if (ret == 1 && shared) + mux->shared = true; + if (ret > 1 && (!shared || !mux->shared)) { + atomic_dec(&mux->use_count); + put_device(&mux_chip->dev); + return ERR_PTR(-EBUSY); + } + + return mux; +} + +/** + * mux_control_get_shared() - Get the mux-control for a device. + * @dev: The device that needs a mux-control. + * @mux_name: The name identifying the mux-control. + * + * The returned mux control is in shared mode and can not be controlled from + * userspace. The mux control lock is taken when the mux is selected and + * released when the mux is deselected. + * + * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno. + */ +struct mux_control *mux_control_get_shared(struct device *dev, + const char *mux_name) +{ + return __mux_control_get(dev, mux_name, true); +} +EXPORT_SYMBOL_GPL(mux_control_get_shared); + +/** + * mux_control_get_exclusive() - Get the mux-control for a device. + * @dev: The device that needs a mux-control. + * @mux_name: The name identifying the mux-control. + * + * The returned mux control is in exclusive mode and does not lock the mux + * control lock when the mux is selected. The exclusive consumer has to take + * care of locking, if necessary. + * + * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno. + */ +struct mux_control *mux_control_get_exclusive(struct device *dev, + const char *mux_name) +{ + return __mux_control_get(dev, mux_name, false); } -EXPORT_SYMBOL_GPL(mux_control_get); +EXPORT_SYMBOL_GPL(mux_control_get_exclusive); /** * mux_control_put() - Put away the mux-control for good. @@ -517,6 +561,7 @@ EXPORT_SYMBOL_GPL(mux_control_get); */ void mux_control_put(struct mux_control *mux) { + atomic_dec(&mux->use_count); put_device(&mux->chip->dev); } EXPORT_SYMBOL_GPL(mux_control_put); @@ -528,16 +573,9 @@ static void devm_mux_control_release(struct device *dev, void *res) mux_control_put(mux); } -/** - * devm_mux_control_get() - Get the mux-control for a device, with resource - * management. - * @dev: The device that needs a mux-control. - * @mux_name: The name identifying the mux-control. - * - * Return: Pointer to the mux-control, or an ERR_PTR with a negative errno. - */ -struct mux_control *devm_mux_control_get(struct device *dev, - const char *mux_name) +static struct mux_control *__devm_mux_control_get(struct device *dev, + const char *mux_name, + bool shared) { struct mux_control **ptr, *mux; @@ -545,7 +583,7 @@ struct mux_control *devm_mux_control_get(struct device *dev, if (!ptr) return ERR_PTR(-ENOMEM); - mux = mux_control_get(dev, mux_name); + mux = __mux_control_get(dev, mux_name, shared); if (IS_ERR(mux)) { devres_free(ptr); return mux; @@ -556,7 +594,36 @@ struct mux_control *devm_mux_control_get(struct device *dev, return mux; } -EXPORT_SYMBOL_GPL(devm_mux_control_get); + +/** + * devm_mux_control_get_shared() - Get the mux-control for a device, with + * resource management. + * @dev: The device that needs a mux-control. + * @mux_name: The name identifying the mux-control. + * + * Return: Pointer to the mux-control, or an ERR_PTR with a negative errno. + */ +struct mux_control *devm_mux_control_get_shared(struct device *dev, + const char *mux_name) +{ + return __devm_mux_control_get(dev, mux_name, true); +} +EXPORT_SYMBOL_GPL(devm_mux_control_get_shared); + +/** + * devm_mux_control_get_exclusive() - Get the mux-control for a device, with + * resource management. + * @dev: The device that needs a mux-control. + * @mux_name: The name identifying the mux-control. + * + * Return: Pointer to the mux-control, or an ERR_PTR with a negative errno. + */ +struct mux_control *devm_mux_control_get_exclusive(struct device *dev, + const char *mux_name) +{ + return __devm_mux_control_get(dev, mux_name, false); +} +EXPORT_SYMBOL_GPL(devm_mux_control_get_exclusive); static int devm_mux_control_match(struct device *dev, void *res, void *data) { diff --git a/include/linux/mux/consumer.h b/include/linux/mux/consumer.h index a2a61834bd3ae..26634c3dda124 100644 --- a/include/linux/mux/consumer.h +++ b/include/linux/mux/consumer.h @@ -23,11 +23,16 @@ int __must_check mux_control_try_select(struct mux_control *mux, unsigned int state); int mux_control_deselect(struct mux_control *mux); -struct mux_control *mux_control_get(struct device *dev, const char *mux_name); +struct mux_control *mux_control_get_exclusive(struct device *dev, + const char *mux_name); +struct mux_control *mux_control_get_shared(struct device *dev, + const char *mux_name); void mux_control_put(struct mux_control *mux); -struct mux_control *devm_mux_control_get(struct device *dev, - const char *mux_name); +struct mux_control *devm_mux_control_get_exclusive(struct device *dev, + const char *mux_name); +struct mux_control *devm_mux_control_get_shared(struct device *dev, + const char *mux_name); void devm_mux_control_put(struct device *dev, struct mux_control *mux); #endif /* _LINUX_MUX_CONSUMER_H */ diff --git a/include/linux/mux/driver.h b/include/linux/mux/driver.h index 95269f40670a7..0ac5d3db9cd3e 100644 --- a/include/linux/mux/driver.h +++ b/include/linux/mux/driver.h @@ -31,17 +31,20 @@ struct mux_control_ops { /** * struct mux_control - Represents a mux controller. - * @lock: Protects the mux controller state. + * @lock: Protects the mux controller state, if shared. * @chip: The mux chip that is handling this mux controller. * @cached_state: The current mux controller state, or -1 if none. * @states: The number of mux controller states. * @idle_state: The mux controller state to use when inactive, or one * of MUX_IDLE_AS_IS and MUX_IDLE_DISCONNECT. + * @use_count: Number of consumers that have requested this mux. + * @shared: True if the mux control was requested as shared and + * must therefore be locked. * * Mux drivers may only change @states and @idle_state, and may only do so * between allocation and registration of the mux controller. Specifically, - * @cached_state is internal to the mux core and should never be written by - * mux drivers. + * @cached_state, @use_count, and @shared are internal to the mux core and + * should never be written by mux drivers. */ struct mux_control { struct mutex lock; /* protects the state of the mux */ @@ -51,6 +54,9 @@ struct mux_control { unsigned int states; int idle_state; + + atomic_t use_count; + bool shared; }; /**