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Date:   Thu, 7 Dec 2017 11:35:45 +0000
From:   Ben Whitten <>
To:     Jacek Anaszewski <>
Subject: Re: [PATCH/RFC v2] leds: trigger: Introduce a NETDEV trigger

On 6 December 2017 at 20:07, Ben Whitten <> wrote:
> Hi Jacek,
> On 5 December 2017 at 20:38, Jacek Anaszewski
> <> wrote:
>> Hi Ben,
>> On 12/05/2017 12:19 PM, Ben Whitten wrote:
>>> From: Ben Whitten <>
>>> The patch was converted to led_blink_oneshot, in doing so we find that the
>>> behaviour has changed. As I dont want to break 'userspace' led behaviour this
>>> patch shouldn't be merged as is. Open to suggestions.
>>> Given an interval of 50ms and heavy throughput, the previous implementation
>>> produced a blink with 100ms period and 50% dutycycle. The led_blink_oneshot
>>> version produces a blink with 140ms period and 57% dutycycle.
>> Please check if the LED class driver you're testing the trigger with
>> implements blink_set op. If yes it would be good to check if it doesn't
>> align the delay intervals to the hardware capabilities instead of
>> failing and relying on a LED core software blink fallback.
> The led are using gpio-led set from device tree on an embedded system, sama5
> based. So as far as I can tell blink_op is NULL in this case and it
> then relies on
> software for the blink in the form of timers.
> I assume its the jiffies playing a part here, taking a jiffy or two to
> queue up a flash
> may add 10ms to the desired 50ms delay_on/delay_off that I am seeing. Then the
> extra time may be due to the stats workqueue not aligning with the
> blink timer to
> kick it off again.

I have found a solution. As oneshot appears run in software regardless
based on the
check in led_blink_setup, cancelling the software timer in the stats
worker allows for
an immidiate requeue. This brings the period back down to 110ms and looks
identical to the previous implementation.

Best regards,

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