linux-kernel - RE: [PATCH 6/6] devfreq: rk3399_dmc: register devfreq notification to dmc driver.

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Date:   Tue, 24 Apr 2018 13:22:33 +0900
From:   MyungJoo Ham <myungjoo.ham@...sung.com>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
CC:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "heiko@...ech.de" <heiko@...ech.de>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "dbasehore@...omium.org" <dbasehore@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dianders@...gle.com" <dianders@...gle.com>,
        "groek@...gle.com" <groek@...gle.com>,
        "kernel@...labora.com" <kernel@...labora.com>,
        Lin Huang <hl@...k-chips.com>,
        Elaine Zhang <zhangqing@...k-chips.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: RE: [PATCH 6/6] devfreq: rk3399_dmc: register devfreq notification
 to dmc driver.

>From: Lin Huang <hl@...k-chips.com>
>
>Because dmc may also access the PMU_BUS_IDLE_REQ register, we need to
>ensure that the pd driver and the dmc driver will not access at this
>register at the same time.
>
>Signed-off-by: Lin Huang <hl@...k-chips.com>
>Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
>---
>
> drivers/devfreq/rk3399_dmc.c      | 47 +----------------------
> drivers/soc/rockchip/pm_domains.c | 31 +++++++++++++++
> include/soc/rockchip/rk3399_dmc.h | 63 +++++++++++++++++++++++++++++++
> 3 files changed, 96 insertions(+), 45 deletions(-)
> create mode 100644 include/soc/rockchip/rk3399_dmc.h
>
>diff --git a/drivers/devfreq/rk3399_dmc.c b/drivers/devfreq/rk3399_dmc.c
>index 5bfca028eaaf..a1f320634d69 100644
>--- a/drivers/devfreq/rk3399_dmc.c
>+++ b/drivers/devfreq/rk3399_dmc.c
[]
>diff --git a/drivers/soc/rockchip/pm_domains.c b/drivers/soc/rockchip/pm_domains.c
>index 53efc386b1ad..7acc836e7eb7 100644
>--- a/drivers/soc/rockchip/pm_domains.c
>+++ b/drivers/soc/rockchip/pm_domains.c
[]
>+static int dmc_notify(struct notifier_block *nb, unsigned long event,
>+		      void *data)
>+{
>+	if (event == DEVFREQ_PRECHANGE)
>+		mutex_lock(&dmc_pmu->mutex);
>+	else if (event == DEVFREQ_POSTCHANGE)
>+		mutex_unlock(&dmc_pmu->mutex);
>+
>+	return NOTIFY_OK;
>+}
>+

Doesn't this incur a deadlock?

1. devfreq.c:update_freq calls devfreq_notify_transition(DEVFREQ_PRECHANGE)
2. pm_domain.c:dmc_notify calls mutex_lock(dmc_pmu->mutex)
3. devfreq.c:update_freq calls target callback
4. rk3399_dmc.c:rk3399_dmcfreq_target calls mutex_lock(&dmcfreq->lock)
   >>>>>> update_freq cannot proceed. <<<<


Cheers,
MyungJoo