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Message-ID: <87tx4ecz10.fsf@intel.com>
Date: Thu, 11 Sep 2014 12:00:27 +0300
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: David Herrmann <dh.herrmann@...il.com>,
dri-devel@...ts.freedesktop.org
Cc: Matthew Garrett <matthew.garrett@...ula.com>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Bryan Wu <cooloney@...il.com>, linux-kernel@...r.kernel.org,
Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH RFC 2/4] backlight: use spin-lock to protect device list
On Wed, 10 Sep 2014, David Herrmann <dh.herrmann@...il.com> wrote:
> There is really no reason to use a mutex to protect a simple list. Convert
> the list-lock to a simple spinlock instead.
>
> The spin-locks prepare for a backlight_find() helper, which should
> preferably be usable from atomic context. A mutex would prevent that, so
> use an irq-save spinlock instead.
>
> Signed-off-by: David Herrmann <dh.herrmann@...il.com>
Reviewed-by: Jani Nikula <jani.nikula@...el.com>
> ---
> drivers/video/backlight/backlight.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 726c6c6..33b64be 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -16,13 +16,14 @@
> #include <linux/err.h>
> #include <linux/fb.h>
> #include <linux/slab.h>
> +#include <linux/spinlock.h>
>
> #ifdef CONFIG_PMAC_BACKLIGHT
> #include <asm/backlight.h>
> #endif
>
> static LIST_HEAD(backlight_dev_list);
> -static DEFINE_MUTEX(backlight_dev_list_mutex);
> +static DEFINE_SPINLOCK(backlight_dev_list_lock);
> static BLOCKING_NOTIFIER_HEAD(backlight_notifier);
>
> static const char *const backlight_types[] = {
> @@ -369,9 +370,9 @@ struct backlight_device *backlight_device_register(const char *name,
> mutex_unlock(&pmac_backlight_mutex);
> #endif
>
> - mutex_lock(&backlight_dev_list_mutex);
> + spin_lock_irq(&backlight_dev_list_lock);
> list_add(&new_bd->entry, &backlight_dev_list);
> - mutex_unlock(&backlight_dev_list_mutex);
> + spin_unlock_irq(&backlight_dev_list_lock);
>
> blocking_notifier_call_chain(&backlight_notifier,
> BACKLIGHT_REGISTERED, new_bd);
> @@ -384,15 +385,16 @@ bool backlight_device_registered(enum backlight_type type)
> {
> bool found = false;
> struct backlight_device *bd;
> + unsigned long flags;
>
> - mutex_lock(&backlight_dev_list_mutex);
> + spin_lock_irqsave(&backlight_dev_list_lock, flags);
> list_for_each_entry(bd, &backlight_dev_list, entry) {
> if (bd->props.type == type) {
> found = true;
> break;
> }
> }
> - mutex_unlock(&backlight_dev_list_mutex);
> + spin_unlock_irqrestore(&backlight_dev_list_lock, flags);
>
> return found;
> }
> @@ -409,9 +411,9 @@ void backlight_device_unregister(struct backlight_device *bd)
> if (!bd)
> return;
>
> - mutex_lock(&backlight_dev_list_mutex);
> + spin_lock_irq(&backlight_dev_list_lock);
> list_del(&bd->entry);
> - mutex_unlock(&backlight_dev_list_mutex);
> + spin_unlock_irq(&backlight_dev_list_lock);
>
> #ifdef CONFIG_PMAC_BACKLIGHT
> mutex_lock(&pmac_backlight_mutex);
> --
> 2.1.0
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Jani Nikula, Intel Open Source Technology Center
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