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From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: William Breathitt Gray <vilhelm.gray@gmail.com>
Cc: Jonathan Cameron <jic23@kernel.org>,
	<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 12:20:00 +0100	[thread overview]
Message-ID: <20210927122000.00007d65@Huawei.com> (raw)
In-Reply-To: <YVGbHQnpBTQYm/7/@shinobu>

On Mon, 27 Sep 2021 19:21:17 +0900
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> 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
> 

It would be less esoteric.  This was the first time I've ever come across the bitlock stuff
whereas atomics are an every day thing.

Thanks,

Jonathan

  reply	other threads:[~2021-09-27 11:20 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 " 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
2021-09-27 11:20           ` Jonathan Cameron [this message]
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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