From patchwork Thu Mar 28 20:59:02 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mike Turquette X-Patchwork-Id: 15758 Return-Path: X-Original-To: patchwork@peony.canonical.com Delivered-To: patchwork@peony.canonical.com Received: from fiordland.canonical.com (fiordland.canonical.com [91.189.94.145]) by peony.canonical.com (Postfix) with ESMTP id 9D49923E39 for ; Thu, 28 Mar 2013 20:59:57 +0000 (UTC) Received: from mail-vc0-f175.google.com (mail-vc0-f175.google.com [209.85.220.175]) by fiordland.canonical.com (Postfix) with ESMTP id 4127EA189B2 for ; Thu, 28 Mar 2013 20:59:57 +0000 (UTC) Received: by mail-vc0-f175.google.com with SMTP id hf12so8004568vcb.6 for ; Thu, 28 Mar 2013 13:59:56 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-received:x-forwarded-to:x-forwarded-for:delivered-to:x-received :received-spf:x-received:from:to:cc:subject:date:message-id:x-mailer :in-reply-to:references:x-gm-message-state; bh=yPI4tK/Atk0rFMPtTDLLuSrhHIEU7WZ0m9SIuR7aNd4=; b=gvvKQZPfsbb76Avg2eMPwm1Td+4OHeFTajA16aS6f6ePy8cbzsbIs0RooPwyfWhAlQ MnHqeP5nhBzK9Qb8zv2Z1O2FZkxc/oUh/6JGmsmSqaWMlTaa8fckoA/SMFUIgbjPL+NV Bt4HczjBMmFAV3/TnoUulClvIbCaGc1mTUxYc78RB9AF6Q6ap+Pw8mOwdU7sGpEKtHkh 4CmpyK+wdHV4c9eT1rZCjfRufeegVfQqLXUBXLr/ScUU7SqKwEYKpuyHMCLGNkbfeUfV h1hLlurgVXPU4evrIng7RxY1J3KTyPhc+xS8oLrCuf2VoAqVl7DpxrJ2CRtItaM3HENs XEVQ== X-Received: by 10.52.31.103 with SMTP id z7mr63801vdh.56.1364504396783; Thu, 28 Mar 2013 13:59:56 -0700 (PDT) X-Forwarded-To: linaro-patchwork@canonical.com X-Forwarded-For: patch@linaro.org linaro-patchwork@canonical.com Delivered-To: patches@linaro.org Received: by 10.59.4.204 with SMTP id cg12csp33264ved; Thu, 28 Mar 2013 13:59:56 -0700 (PDT) X-Received: by 10.68.221.36 with SMTP id qb4mr124533pbc.66.1364504395556; Thu, 28 Mar 2013 13:59:55 -0700 (PDT) Received: from mail-pa0-f51.google.com (mail-pa0-f51.google.com [209.85.220.51]) by mx.google.com with ESMTPS id hi1si838715pac.0.2013.03.28.13.59.55 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 28 Mar 2013 13:59:55 -0700 (PDT) Received-SPF: neutral (google.com: 209.85.220.51 is neither permitted nor denied by best guess record for domain of mturquette@linaro.org) client-ip=209.85.220.51; Authentication-Results: mx.google.com; spf=neutral (google.com: 209.85.220.51 is neither permitted nor denied by best guess record for domain of mturquette@linaro.org) smtp.mail=mturquette@linaro.org Received: by mail-pa0-f51.google.com with SMTP id jh10so75050pab.24 for ; Thu, 28 Mar 2013 13:59:55 -0700 (PDT) X-Received: by 10.66.228.74 with SMTP id sg10mr904155pac.48.1364504395105; Thu, 28 Mar 2013 13:59:55 -0700 (PDT) Received: from quantum.gateway.2wire.net (adsl-69-228-93-79.dsl.pltn13.pacbell.net. [69.228.93.79]) by mx.google.com with ESMTPS id qe3sm163973pbb.0.2013.03.28.13.59.52 (version=TLSv1.1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 28 Mar 2013 13:59:54 -0700 (PDT) From: Mike Turquette To: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, patches@linaro.org, linaro-kernel@lists.linaro.org, rajagopal.venkat@linaro.org, davidb@codeaurora.org, ulf.hansson@linaro.org, laurent.pinchart@ideasonboard.com, tglx@linutronix.de, Mike Turquette Subject: [PATCH 2/2] clk: allow reentrant calls into the clk framework Date: Thu, 28 Mar 2013 13:59:02 -0700 Message-Id: <1364504343-12635-3-git-send-email-mturquette@linaro.org> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <1364504343-12635-1-git-send-email-mturquette@linaro.org> References: <1364445958-2999-1-git-send-email-mturquette@linaro.org> <1364504343-12635-1-git-send-email-mturquette@linaro.org> X-Gm-Message-State: ALoCoQm2SX9awUaRlOmKbMsnhdNheQJKodxHpCg77yRnYk1H5Od6yQkgdzVWjVVe9N4TNIZQTmuK Reentrancy into the clock framework is necessary for clock operations that result in nested calls to the clk api. A common example is a clock that is prepared via an i2c transaction, such as a clock inside of a discrete audio chip or a power management IC. The i2c subsystem itself will use the clk api resulting in a deadlock: clk_prepare(audio_clk) i2c_transfer(..) clk_prepare(i2c_controller_clk) The ability to reenter the clock framework prevents this deadlock. Other use cases exist such as allowing .set_rate callbacks to call clk_set_parent to achieve the best rate, or to save power in certain configurations. Yet another example is performing pinctrl operations from a clk_ops callback. Calls into the pinctrl subsystem may call clk_{un}prepare on an unrelated clock. Allowing for nested calls to reenter the clock framework enables both of these use cases. Reentrancy is implemented by two global pointers that track the owner currently holding a global lock. One pointer tracks the owner during sleepable, mutex-protected operations and the other one tracks the owner during non-interruptible, spinlock-protected operations. When the clk framework is entered we try to hold the global lock. If it is held we compare the current task against the current owner; a match implies a nested call and we reenter. If the values do not match then we block on the lock until it is released. Signed-off-by: Mike Turquette Cc: Rajagopal Venkat Cc: David Brown Cc: Ulf Hansson Tested-by: Laurent Pinchart Reviewed-by: Thomas Gleixner Reviewed-by: Ulf Hansson --- Changes since v5: * fixed up typo in changelog Changes since v4: * remove uneccesary atomic operations * remove casting bugs * place reentrancy logic into locking helper functions * improve debugging with reference counting and WARNs drivers/clk/clk.c | 44 ++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 42 insertions(+), 2 deletions(-) diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index 0b5d612..0230c9d 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -19,10 +19,17 @@ #include #include #include +#include static DEFINE_SPINLOCK(enable_lock); static DEFINE_MUTEX(prepare_lock); +static struct task_struct *prepare_owner; +static struct task_struct *enable_owner; + +static int prepare_refcnt; +static int enable_refcnt; + static HLIST_HEAD(clk_root_list); static HLIST_HEAD(clk_orphan_list); static LIST_HEAD(clk_notifier_list); @@ -30,23 +37,56 @@ static LIST_HEAD(clk_notifier_list); /*** locking ***/ static void clk_prepare_lock(void) { - mutex_lock(&prepare_lock); + if (!mutex_trylock(&prepare_lock)) { + if (prepare_owner == current) { + prepare_refcnt++; + return; + } + mutex_lock(&prepare_lock); + } + WARN_ON_ONCE(prepare_owner != NULL); + WARN_ON_ONCE(prepare_refcnt != 0); + prepare_owner = current; + prepare_refcnt = 1; } static void clk_prepare_unlock(void) { + WARN_ON_ONCE(prepare_owner != current); + WARN_ON_ONCE(prepare_refcnt == 0); + + if (--prepare_refcnt) + return; + prepare_owner = NULL; mutex_unlock(&prepare_lock); } static unsigned long clk_enable_lock(void) { unsigned long flags; - spin_lock_irqsave(&enable_lock, flags); + + if (!spin_trylock_irqsave(&enable_lock, flags)) { + if (enable_owner == current) { + enable_refcnt++; + return flags; + } + spin_lock_irqsave(&enable_lock, flags); + } + WARN_ON_ONCE(enable_owner != NULL); + WARN_ON_ONCE(enable_refcnt != 0); + enable_owner = current; + enable_refcnt = 1; return flags; } static void clk_enable_unlock(unsigned long flags) { + WARN_ON_ONCE(enable_owner != current); + WARN_ON_ONCE(enable_refcnt == 0); + + if (--enable_refcnt) + return; + enable_owner = NULL; spin_unlock_irqrestore(&enable_lock, flags); }