From: William Breathitt Gray <vilhelm.gray@gmail.com>
To: David Lechner <david@lechnology.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: Sun, 18 Oct 2020 12:58:22 -0400 [thread overview]
Message-ID: <20201018165822.GE231549@shinobu> (raw)
In-Reply-To: <cc1f7e4d-18d1-bc28-8ce3-e3edcd91bcab@lechnology.com>
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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.
William Breathitt Gray
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next prev parent reply other threads:[~2020-10-18 16:58 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-27 2:18 [PATCH v5 0/5] Introduce the Counter character device interface William Breathitt Gray
2020-09-27 2:18 ` [PATCH v5 1/5] counter: Internalize sysfs interface code William Breathitt Gray
2020-10-13 2:15 ` 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
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 [this message]
2020-10-20 16:06 ` David Lechner
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
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