From: William Breathitt Gray <vilhelm.gray@gmail.com>
To: Jonathan Cameron <jic23@kernel.org>
Cc: linux-stm32@st-md-mailman.stormreply.com, kernel@pengutronix.de,
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, jarkko.nikula@linux.intel.com,
Dan Carpenter <dan.carpenter@oracle.com>
Subject: Re: [PATCH v16 07/14] counter: Add character device interface
Date: Mon, 27 Sep 2021 19:21:17 +0900 [thread overview]
Message-ID: <YVGbHQnpBTQYm/7/@shinobu> (raw)
In-Reply-To: <20210926161542.5cf99b58@jic23-huawei>
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On Sun, Sep 26, 2021 at 04:15:42PM +0100, Jonathan Cameron wrote:
> On Mon, 20 Sep 2021 19:09:13 +0900
> William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
>
> > On Sun, Sep 12, 2021 at 05:18:42PM +0100, Jonathan Cameron wrote:
> > > On Fri, 27 Aug 2021 12:47:51 +0900
> > > William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
> > >
> > > > This patch introduces a character device interface for the Counter
> > > > subsystem. Device data is exposed through standard character device read
> > > > operations. Device data is gathered when a Counter event is pushed by
> > > > the respective Counter device driver. Configuration is handled via ioctl
> > > > operations on the respective Counter character device node.
> > > >
> > > > Cc: David Lechner <david@lechnology.com>
> > > > Cc: Gwendal Grignou <gwendal@chromium.org>
> > > > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > > > Cc: Oleksij Rempel <o.rempel@pengutronix.de>
> > > > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
> > >
> > > Hi William,
> > >
> > > Why the bit based lock? It feels like a mutex_trylock() type approach or
> > > spinlock_trylock() would be a more common solution to this problem.
> > > There is precedence for doing what you have here though so I'm not that
> > > worried about it.
> >
> > Hi Jonathan,
> >
> > We originally used a mutex for this, but Jarkko discovered that this
> > produced a warning because chrdev_lock would be held when returning to
> > user space:
> > https://lore.kernel.org/linux-arm-kernel/YOq19zTsOzKA8v7c@shinobu/T/#m6072133d418d598a5f368bb942c945e46cfab9a5
> >
> > Following David Lechner's suggestion, I decided to reimplement
> > chrdev_lock as a bitmap using an atomic flag.
>
> Ok. I'm not sure bit lock was quite what was intended (as there is only one of them)
> but I suppose it doesn't greatly matter.
It didn't cross my mind before, but would declaring chrdev_lock as an
atomic_t be a more appropriate solution here because we have only one
flag?
William Breathitt Gray
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next prev parent reply other threads:[~2021-09-27 10:21 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 3:47 [PATCH v16 00/14] Introduce the Counter character device interface William Breathitt Gray
2021-08-27 3:47 ` [PATCH v16 01/14] counter: stm32-lptimer-cnt: Provide defines for clock polarities William Breathitt Gray
2021-08-31 13:38 ` Fabrice Gasnier
2021-09-08 17:31 ` Jonathan Cameron
2021-08-27 3:47 ` [PATCH v16 02/14] counter: stm32-timer-cnt: Provide defines for slave mode selection William Breathitt Gray
2021-08-31 13:40 ` Fabrice Gasnier
2021-09-08 17:31 ` Jonathan Cameron
2021-08-27 3:47 ` [PATCH v16 03/14] counter: Internalize sysfs interface code William Breathitt Gray
2021-08-31 13:44 ` [Linux-stm32] " Fabrice Gasnier
2021-08-31 14:16 ` William Breathitt Gray
2021-08-31 14:55 ` William Breathitt Gray
2021-09-08 17:44 ` Jonathan Cameron
2021-08-27 3:47 ` [PATCH v16 04/14] counter: Update counter.h comments to reflect sysfs internalization William Breathitt Gray
2021-09-08 17:46 ` Jonathan Cameron
2021-08-27 3:47 ` [PATCH v16 05/14] docs: counter: Update " William Breathitt Gray
2021-09-08 17:48 ` Jonathan Cameron
2021-08-27 3:47 ` [PATCH v16 06/14] counter: Move counter enums to uapi header William Breathitt Gray
2021-08-27 3:47 ` [PATCH v16 07/14] counter: Add character device interface William Breathitt Gray
2021-09-12 16:18 ` Jonathan Cameron
2021-09-20 10:09 ` William Breathitt Gray
2021-09-26 15:15 ` Jonathan Cameron
2021-09-27 10:21 ` William Breathitt Gray [this message]
2021-09-27 11:20 ` Jonathan Cameron
2021-09-27 11:33 ` William Breathitt Gray
2021-08-27 3:47 ` [PATCH v16 08/14] docs: counter: Document " William Breathitt Gray
2021-09-12 16:18 ` Jonathan Cameron
2021-08-27 3:47 ` [PATCH v16 09/14] tools/counter: Create Counter tools William Breathitt Gray
2021-09-12 16:26 ` Jonathan Cameron
2021-08-27 3:47 ` [PATCH v16 10/14] counter: Implement signalZ_action_component_id sysfs attribute William Breathitt Gray
2021-08-27 3:47 ` [PATCH v16 11/14] counter: Implement *_component_id sysfs attributes William Breathitt Gray
2021-08-27 3:47 ` [PATCH v16 12/14] counter: Implement events_queue_size sysfs attribute William Breathitt Gray
2021-08-27 3:47 ` [PATCH v16 13/14] counter: 104-quad-8: Replace mutex with spinlock William Breathitt Gray
2021-08-27 3:47 ` [PATCH v16 14/14] counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 William Breathitt Gray
2021-08-30 17:17 ` [PATCH v16 00/14] Introduce the Counter character device interface Jonathan Cameron
2021-09-12 16:36 ` Jonathan Cameron
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