From: Jonathan Liu <net147@gmail.com>
To: oliver@schinagl.nl
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>,
Thierry Reding <thierry.reding@gmail.com>,
Maxime Ripard <maxime.ripard@free-electrons.com>,
Chen-Yu Tsai <wens@csie.org>,
linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [1/2] pwm: sunxi: allow the pwm to finish its pulse before disable
Date: Sat, 24 Sep 2016 00:02:13 +1000 [thread overview]
Message-ID: <CANwerB2LwWShNEUmNNbuH_4GY90gSpVmrxbC+oLK4p51cxUe2g@mail.gmail.com> (raw)
In-Reply-To: <1472147411-30424-2-git-send-email-oliver@schinagl.nl>
On 26 August 2016 at 03:50, <oliver@schinagl.nl> wrote:
> When we inform the PWM block to stop toggeling the output, we may end up
> in a state where the output is not what we would expect (e.g. not the
> low-pulse) but whatever the output was at when the clock got disabled.
>
> To counter this we have to wait for maximally the time of one whole
> period to ensure the pwm hardware was able to finish. Since we already
> told the PWM hardware to disable it self, it will not continue toggling
> but merly finish its current pulse.
>
> If a whole period is considered to much, it may be contemplated to use a
> half period + a little bit to ensure we get passed the transition.
>
> Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
> ---
> drivers/pwm/pwm-sun4i.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> index 03a99a5..5e97c8a 100644
> --- a/drivers/pwm/pwm-sun4i.c
> +++ b/drivers/pwm/pwm-sun4i.c
> @@ -8,6 +8,7 @@
>
> #include <linux/bitops.h>
> #include <linux/clk.h>
> +#include <linux/delay.h>
> #include <linux/err.h>
> #include <linux/io.h>
> #include <linux/module.h>
> @@ -245,6 +246,16 @@ static void sun4i_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> spin_lock(&sun4i_pwm->ctrl_lock);
> val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> val &= ~BIT_CH(PWM_EN, pwm->hwpwm);
> + sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> + spin_unlock(&sun4i_pwm->ctrl_lock);
> +
> + /* Allow for the PWM hardware to finish its last toggle. The pulse
> + * may have just started and thus we should wait a full period.
> + */
> + ndelay(pwm_get_period(pwm));
> +
> + spin_lock(&sun4i_pwm->ctrl_lock);
> + val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> spin_unlock(&sun4i_pwm->ctrl_lock);
I had some issues where setting the brightness for pwm-backlight to 0
was not turning off the backlight sometimes.
This patch fixes the issue for me. Thanks.
Tested-by: Jonathan Liu <net147@gmail.com>
next prev parent reply other threads:[~2016-09-23 14:02 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-25 17:50 [PATCHv2 0/2] pwm: sunxi: give the pwm IP block more time Olliver Schinagl
2016-08-25 17:50 ` [PATCH 1/2] pwm: sunxi: allow the pwm to finish its pulse before disable Olliver Schinagl
2016-08-26 22:19 ` Maxime Ripard
2016-09-06 7:12 ` Olliver Schinagl
2016-09-06 19:51 ` Maxime Ripard
2016-09-09 9:01 ` Olliver Schinagl
2016-09-24 20:25 ` Maxime Ripard
2016-09-26 8:46 ` Olliver Schinagl
2016-09-27 20:16 ` Maxime Ripard
[not found] ` <afcb938d-d2df-4740-6c85-cdf2766f671c@schinagl.nl>
2016-12-12 12:24 ` Maxime Ripard
2017-01-03 15:59 ` Olliver Schinagl
2017-01-03 16:55 ` Alexandre Belloni
2017-01-04 6:36 ` Thierry Reding
2016-09-23 14:02 ` Jonathan Liu [this message]
2016-09-23 14:03 ` [1/2] " Olliver Schinagl
2017-05-05 1:54 ` Jonathan Liu
2016-08-25 17:50 ` [PATCH 2/2] pwm: sunxi: Yield some time to the pwm-block to become ready Olliver Schinagl
2016-08-26 22:25 ` Maxime Ripard
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=CANwerB2LwWShNEUmNNbuH_4GY90gSpVmrxbC+oLK4p51cxUe2g@mail.gmail.com \
--to=net147@gmail.com \
--cc=alexandre.belloni@free-electrons.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pwm@vger.kernel.org \
--cc=maxime.ripard@free-electrons.com \
--cc=oliver@schinagl.nl \
--cc=thierry.reding@gmail.com \
--cc=wens@csie.org \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).