Linux-IIO Archive on lore.kernel.org
 help / color / Atom feed
From: David Lechner <david@lechnology.com>
To: William Breathitt Gray <vilhelm.gray@gmail.com>
Cc: jic23@kernel.org, kamel.bouhara@bootlin.com,
	gwendal@chromium.org, alexandre.belloni@bootlin.com,
	linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	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
Subject: Re: [PATCH v5 3/5] counter: Add character device interface
Date: Tue, 20 Oct 2020 11:06:42 -0500
Message-ID: <f2bac8b2-108d-fa4c-cb63-8ff85ce04d1f@lechnology.com> (raw)
In-Reply-To: <20201018165822.GE231549@shinobu>

On 10/18/20 11:58 AM, William Breathitt Gray wrote:
> On Wed, Oct 14, 2020 at 05:40:44PM -0500, David Lechner wrote:
>> On 9/26/20 9:18 PM, William Breathitt Gray wrote:
>>> +static ssize_t counter_chrdev_read(struct file *filp, char __user *buf,
>>> +				   size_t len, loff_t *f_ps)
>>> +{
>>> +	struct counter_device *const counter = filp->private_data;
>>> +	int err;
>>> +	unsigned long flags;
>>> +	unsigned int copied;
>>> +
>>> +	if (len < sizeof(struct counter_event))
>>> +		return -EINVAL;
>>> +
>>> +	do {
>>> +		if (kfifo_is_empty(&counter->events)) {
>>> +			if (filp->f_flags & O_NONBLOCK)
>>> +				return -EAGAIN;
>>> +
>>> +			err = wait_event_interruptible(counter->events_wait,
>>> +					!kfifo_is_empty(&counter->events));
>>> +			if (err)
>>> +				return err;
>>> +		}
>>> +
>>> +		raw_spin_lock_irqsave(&counter->events_lock, flags);
>>> +		err = kfifo_to_user(&counter->events, buf, len, &copied);
>>> +		raw_spin_unlock_irqrestore(&counter->events_lock, flags);
>>> +		if (err)
>>> +			return err;
>>> +	} while (!copied);
>>> +
>>> +	return copied;
>>> +}
>>
>> All other uses of kfifo_to_user() I saw use a mutex instead of spin
>> lock. I don't see a reason for disabling interrupts here.
> 
> The Counter character device interface is special in this case because
> counter->events could be accessed from an interrupt context. This is
> possible if counter_push_event() is called for an interrupt (as is the
> case for the 104_quad_8 driver). In this case, we can't use mutex
> because we can't sleep in an interrupt context, so our only option is to
> use spin lock.
> 


The way I understand it, locking is only needed for concurrent readers
and locking between reader and writer is not needed.

  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-27  2:18 [PATCH v5 0/5] Introduce the Counter " William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 2/5] docs: counter: Update to reflect sysfs internalization William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 3/5] counter: Add character device interface William Breathitt Gray
2020-10-14  1:40   ` David Lechner
2020-10-18 16:49     ` William Breathitt Gray
2020-10-20 15:53       ` David Lechner
2020-10-25 12:55         ` William Breathitt Gray
2020-10-25 16:36           ` David Lechner
2020-10-14 17:43   ` David Lechner
2020-10-14 19:05     ` William Breathitt Gray
2020-10-14 22:32       ` David Lechner
2020-10-14 22:40   ` David Lechner
2020-10-18 16:58     ` William Breathitt Gray
2020-10-20 16:06       ` David Lechner [this message]
2020-10-25 13:18         ` William Breathitt Gray
2020-10-25 16:34           ` David Lechner
2020-10-25 17:53             ` William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 4/5] docs: counter: Document " William Breathitt Gray
2020-10-08  8:09   ` Pavel Machek
2020-10-08 12:28     ` William Breathitt Gray
2020-10-12 17:04       ` David Lechner
2020-10-13 18:58         ` William Breathitt Gray
2020-10-13 19:08           ` David Lechner
2020-10-13 19:27             ` William Breathitt Gray
2020-09-27  2:18 ` [PATCH v5 5/5] counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 William Breathitt Gray
2020-10-14  0:13   ` David Lechner
2020-10-18 14:50     ` William Breathitt Gray
2020-10-13  0:35 ` [PATCH v5 0/5] Introduce the Counter character device interface David Lechner
2020-10-18 14:14   ` William Breathitt Gray
     [not found] ` <e38f6dc3a08bf2510034334262776a6ed1df8b89.1601170670.git.vilhelm.gray@gmail.com>
2020-10-13  2:15   ` [PATCH v5 1/5] counter: Internalize sysfs interface code David Lechner
2020-10-18 14:49     ` William Breathitt Gray
2020-10-20 15:38       ` David Lechner
2020-10-23 13:12         ` William Breathitt Gray
2020-10-15  1:38   ` David Lechner
2020-10-18 17:00     ` William Breathitt Gray

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=f2bac8b2-108d-fa4c-cb63-8ff85ce04d1f@lechnology.com \
    --to=david@lechnology.com \
    --cc=alexandre.belloni@bootlin.com \
    --cc=alexandre.torgue@st.com \
    --cc=fabrice.gasnier@st.com \
    --cc=gwendal@chromium.org \
    --cc=jic23@kernel.org \
    --cc=kamel.bouhara@bootlin.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-iio@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-stm32@st-md-mailman.stormreply.com \
    --cc=mcoquelin.stm32@gmail.com \
    --cc=patrick.havelange@essensium.com \
    --cc=syednwaris@gmail.com \
    --cc=vilhelm.gray@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-IIO Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-iio/0 linux-iio/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-iio linux-iio/ https://lore.kernel.org/linux-iio \
		linux-iio@vger.kernel.org
	public-inbox-index linux-iio

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-iio


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git