From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bjorn Andersson <bjorn.andersson@linaro.org>
Subject: Re: [PATCH] pinctrl: qcom: Use raw spinlock variants
Date: Fri, 20 Jan 2017 10:04:40 -0800
Message-ID: <20170120180440.GY10531@minitux>
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To: Julia Cartwright <julia@ni.com>
Cc: Linus Walleij <linus.walleij@linaro.org>, Brian Wrenn <dcbrianw@gmail.com>, linux-rt-users@vger.kernel.org, "linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>, "open list:ARM/QUALCOMM SUPPORT" <linux-soc@vger.kernel.org>, "linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>, Andy Gross <andy.gross@linaro.org>, David Brown <david.brown@linaro.org>
List-Id: linux-gpio@vger.kernel.org

On Fri 20 Jan 08:13 PST 2017, Julia Cartwright wrote:

> The MSM pinctrl driver currently implements an irq_chip for handling
> GPIO interrupts; due to how irq_chip handling is done, it's necessary
> for the irq_chip methods to be invoked from hardirq context, even on a
> a real-time kernel.  Because the spinlock_t type becomes a "sleeping"
> spinlock w/ RT kernels, it is not suitable to be used with irq_chips.
> 

Thanks for the explanation.

> A quick audit of the operations under the lock reveal that they do only
> minimal, bounded work, and are therefore safe to do under a raw
> spinlock.
> 

I agree with this conclusion.

> On real-time kernels, this fixes an OOPs which looks like the following,
> as reported by Brian Wrenn:
> 
>     kernel BUG at kernel/locking/rtmutex.c:1014!
>     Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>     Modules linked in: spidev_irq(O) smsc75xx wcn36xx [last unloaded: spidev]
>     CPU: 0 PID: 1163 Comm: irq/144-mmc0 Tainted: G        W  O    4.4.9-linaro-lt-qcom #1
>     PC is at rt_spin_lock_slowlock+0x80/0x2d8
>     LR is at rt_spin_lock_slowlock+0x68/0x2d8
>     [..]
>   Call trace:
>     rt_spin_lock_slowlock
>     rt_spin_lock
>     msm_gpio_irq_ack
>     handle_edge_irq
>     generic_handle_irq
>     msm_gpio_irq_handler
>     generic_handle_irq
>     __handle_domain_irq
>     gic_handle_irq
> 
> Cc: Bjorn Andersson <bjorn.andersson@linaro.org>

Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Regards,
Bjorn