From: j.anaszewski@samsung•com (Jacek Anaszewski)
To: linux-arm-kernel@lists•infradead.org
Subject: [RESEND PATCH 3/4] leds: leds-ns2: handle can_sleep GPIOs
Date: Mon, 29 Jun 2015 16:25:13 +0200 [thread overview]
Message-ID: <55915549.60106@samsung.com> (raw)
In-Reply-To: <20150626171028.GL4853@kw.sim.vm.gnt>
On 06/26/2015 07:10 PM, Simon Guinot wrote:
> On Wed, Jun 24, 2015 at 04:18:29PM +0200, Jacek Anaszewski wrote:
>> On 06/18/2015 05:17 PM, Simon Guinot wrote:
>>> On the board n090401 (Seagate NAS 4-Bay), some of the LEDs are handled
>>> by the leds-ns2 driver. This LEDs are connected to an I2C GPIO expander
>>> (PCA95554PW) which means that GPIO access may sleep. This patch makes
>>> leds-ns2 compatible with such GPIOs by using the *_cansleep() variant of
>>> the GPIO functions. As a drawback this functions can't be used safely in
>>> a timer context (with the timer LED trigger for example). To fix this
>>> issue, a workqueue mechanism (copied from the leds-gpio driver) is used.
>>>
>>> Note that this patch also updates slightly the ns2_led_sata_store
>>> function. The LED state is now retrieved from cached values instead of
>>> reading the GPIOs previously. This prevents ns2_led_sata_store from
>>> working with a stale LED state (which may happen when a delayed work
>>> is pending).
>>>
>>> Signed-off-by: Simon Guinot <simon.guinot@sequanux•org>
>>> Signed-off-by: Vincent Donnefort <vdonnefort@gmail•com>
>>> ---
>>> drivers/leds/leds-ns2.c | 56 ++++++++++++++++++++++++++++++++++++-------------
>>> 1 file changed, 42 insertions(+), 14 deletions(-)
>>>
>>
>>>
>>> +static void ns2_led_work(struct work_struct *work)
>>> +{
>>> + struct ns2_led_data *led_dat =
>>> + container_of(work, struct ns2_led_data, work);
>>> + int i = led_dat->new_mode_index;
>>> +
>>> + write_lock(&led_dat->rw_lock);
>>> +
>>> + gpio_set_value_cansleep(led_dat->cmd, led_dat->modval[i].cmd_level);
>>> + gpio_set_value_cansleep(led_dat->slow, led_dat->modval[i].slow_level);
>>> +
>>> + write_unlock(&led_dat->rw_lock);
>>> +}
>>> +
>>
>> I've just realized that this can break one of the basic rules:
>> no sleeping should occur while holding a spinlock. Did you
>> consider this?
>
> Well, if I did, I can't say I have done a good job here :/
>
> You have to know that this code is used on a large number of boards.
> Thus, I have to thank you for spotting this bug.As a relief, this don't
> actually lead to a bug with the configuration we are using: UP machine
> and !CONFIG_SMP.
>
> It should be simple to fix it because using a spinlock in ns2_led_work()
> is not needed. The GPIO writing calls are protected by the workqueue
> itself: a single instance is running at a time. We are only let with the
> new_mode_index reading which must be made coherent.
>
> Note that the very same issue also applies to ns2_led_get_mode(). And
> again using a lock here is not needed either. This function is only
> called once at probe time and there is no possible concurrency.
Switching to gpio_get_value_cansleep would be nice there too.
>
> I'll fix all this issues with the v2.
>
> Thanks.
>
> Simon
>
--
Best Regards,
Jacek Anaszewski
next prev parent reply other threads:[~2015-06-29 14:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-18 15:17 [RESEND PATCH 0/4] Allow to use leds-ns2 with n090401 boards Simon Guinot
2015-06-18 15:17 ` [RESEND PATCH 1/4] leds: leds-ns2: move LED modes mapping outside of the driver Simon Guinot
2015-06-22 14:32 ` Jacek Anaszewski
2015-06-23 18:12 ` Simon Guinot
2015-06-24 7:34 ` Jacek Anaszewski
2015-06-18 15:17 ` [RESEND PATCH 2/4] ARM: Kirkwood: add modes-map property to ns2-leds nodes Simon Guinot
2015-06-18 15:17 ` [RESEND PATCH 3/4] leds: leds-ns2: handle can_sleep GPIOs Simon Guinot
2015-06-22 14:33 ` Jacek Anaszewski
2015-06-24 14:18 ` Jacek Anaszewski
2015-06-26 17:10 ` Simon Guinot
2015-06-29 14:25 ` Jacek Anaszewski [this message]
2015-06-29 14:41 ` Simon Guinot
2015-06-18 15:17 ` [RESEND PATCH 4/4] leds: leds-ns2: depends on MACH_ARMADA_370 Simon Guinot
2015-06-22 14:33 ` Jacek Anaszewski
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