From: William Breathitt Gray <vilhelm.gray@gmail.com>
To: Jonathan Cameron <jic23@kernel.org>
Cc: kernel@pengutronix.de, linux-stm32@st-md-mailman.stormreply.com,
a.fatoum@pengutronix.de, kamel.bouhara@bootlin.com,
gwendal@chromium.org, alexandre.belloni@bootlin.com,
david@lechnology.com, linux-iio@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com,
patrick.havelange@essensium.com, fabrice.gasnier@st.com,
mcoquelin.stm32@gmail.com, alexandre.torgue@st.com,
o.rempel@pengutronix.de
Subject: Re: [PATCH v8 21/22] counter: 104-quad-8: Replace mutex with spinlock
Date: Thu, 18 Feb 2021 19:16:08 +0900 [thread overview]
Message-ID: <YC4+aMA6fom7pd4F@shinobu> (raw)
In-Reply-To: <20210216192720.75082d22@archlinux>
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On Tue, Feb 16, 2021 at 07:27:20PM +0000, Jonathan Cameron wrote:
> On Tue, 16 Feb 2021 11:16:03 +0900
> William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
>
> > On Sun, Feb 14, 2021 at 06:19:46PM +0000, Jonathan Cameron wrote:
> > > On Fri, 12 Feb 2021 21:13:45 +0900
> > > William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
> > >
> > > > This patch replaces the mutex I/O lock with a spinlock. This is in
> > > > preparation for a subsequent patch adding IRQ support for 104-QUAD-8
> > > > devices; we can't sleep in an interrupt context, so we'll need to use a
> > > > spinlock instead.
> > > >
> > > > Cc: Syed Nayyar Waris <syednwaris@gmail.com>
> > > > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
> > >
> > > Why do these need to be raw_spin_locks?
> > > Normally only need to do that if in code related to interrupt chips etc,
> > > not their use.
> > >
> > > Jonathan
> >
> > This lock can be taken in an interrupt context in a subsequent patch:
> > counter_push_event() called by quad8_irq_handler() can end up calling
> > the Counter component callbacks which take this lock. We can't use a
> > mutex nor a regular spinlock because those can sleep on RT setups [1]
>
> But on RT setups the interrupts become threads and are preemptable etc,
> so that shouldn't matter. There are a few corner cases that cause
> trouble, but in most normal drivers you should be fine with a
> spin_lock.
>
> Jonathan
Thinking this over again I realize you're probably right. A simple
spin_lock should be fine for these drivers, so I'll switch over to that
instead of the raw_spin_lock for this driver and the Counter interface
code.
William Breathitt Gray
> > which would result in a deadlock due to the interrupt context here -- so
> > therefore we're left with using raw_spin_lock.
> >
> > [1] https://lwn.net/Articles/367219/
> >
> > William Breathitt Gray
>
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next prev parent reply other threads:[~2021-02-18 11:55 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-12 12:13 [PATCH v8 00/22] Introduce the Counter character device interface William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 01/22] docs: counter: Consolidate Counter sysfs attributes documentation William Breathitt Gray
2021-02-14 16:57 ` Jonathan Cameron
2021-02-15 11:05 ` William Breathitt Gray
2021-02-20 16:25 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 02/22] docs: counter: Fix spelling William Breathitt Gray
2021-02-20 16:26 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 03/22] counter: 104-quad-8: Return error when invalid mode during ceiling_write William Breathitt Gray
2021-02-20 16:30 ` David Lechner
2021-02-22 2:06 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 04/22] counter: 104-quad-8: Annotate hardware config module parameter William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 05/22] counter: 104-quad-8: Add const qualifiers for quad8_preset_register_set William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 06/22] counter: 104-quad-8: Add const qualifier for functions_list array William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 07/22] counter: 104-quad-8: Add const qualifier for actions_list array William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 08/22] counter: ftm-quaddec: " William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 09/22] counter: Return error code on invalid modes William Breathitt Gray
2021-02-14 17:07 ` Jonathan Cameron
2021-02-20 16:43 ` David Lechner
2021-02-22 4:42 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 10/22] counter: Standardize to ERANGE for limit exceeded errors William Breathitt Gray
2021-02-14 17:10 ` Jonathan Cameron
2021-02-16 1:26 ` William Breathitt Gray
2021-02-21 14:03 ` Jonathan Cameron
2021-02-20 16:48 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 11/22] counter: Rename counter_signal_value to counter_signal_level William Breathitt Gray
2021-02-20 16:52 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 12/22] counter: Rename counter_count_function to counter_function William Breathitt Gray
2021-02-14 17:13 ` Jonathan Cameron
2021-02-20 16:56 ` David Lechner
2021-02-23 5:14 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 14/22] counter: Update counter.h comments to reflect sysfs internalization William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 15/22] docs: counter: Update " William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 16/22] counter: Move counter enums to uapi header William Breathitt Gray
2021-02-20 23:55 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 17/22] counter: Add character device interface William Breathitt Gray
2021-02-14 18:06 ` Jonathan Cameron
2021-02-24 5:34 ` William Breathitt Gray
2021-02-15 9:24 ` Oleksij Rempel
2021-02-16 1:53 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 18/22] docs: counter: Document " William Breathitt Gray
2021-02-14 17:48 ` Jonathan Cameron
2021-02-22 10:11 ` Pavel Machek
2021-02-26 0:27 ` William Breathitt Gray
2021-02-26 0:22 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 19/22] counter: Implement extension*_name sysfs attributes William Breathitt Gray
2021-02-14 18:09 ` Jonathan Cameron
2021-02-19 8:51 ` William Breathitt Gray
2021-02-21 14:05 ` Jonathan Cameron
2021-02-25 23:32 ` William Breathitt Gray
2021-02-27 15:14 ` Jonathan Cameron
2021-02-12 12:13 ` [PATCH v8 20/22] counter: Implement events_queue_size sysfs attribute William Breathitt Gray
2021-02-14 18:11 ` Jonathan Cameron
2021-02-18 10:32 ` William Breathitt Gray
2021-02-21 15:51 ` Jonathan Cameron
2021-02-26 0:03 ` William Breathitt Gray
2021-02-27 0:14 ` David Lechner
2021-02-27 0:20 ` William Breathitt Gray
2021-02-27 15:18 ` Jonathan Cameron
2021-02-28 2:46 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 21/22] counter: 104-quad-8: Replace mutex with spinlock William Breathitt Gray
2021-02-14 18:19 ` Jonathan Cameron
2021-02-16 2:16 ` William Breathitt Gray
2021-02-16 19:27 ` Jonathan Cameron
2021-02-18 10:16 ` William Breathitt Gray [this message]
2021-02-12 12:13 ` [PATCH v8 22/22] counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 William Breathitt Gray
2021-02-14 18:24 ` Jonathan Cameron
2021-02-19 9:21 ` William Breathitt Gray
[not found] ` <3fc2580af0efd6312a64a0e107bd6fa758f0d466.1613131238.git.vilhelm.gray@gmail.com>
2021-02-14 17:32 ` [PATCH v8 13/22] counter: Internalize sysfs interface code Jonathan Cameron
2021-02-20 17:50 ` David Lechner
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