From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Marco Felsch <m.felsch@pengutronix.de>
Cc: thierry.reding@gmail.com, lee.jones@linaro.org,
shawnguo@kernel.org, s.hauer@pengutronix.de, festevam@gmail.com,
linux-imx@nxp.com, Anson.Huang@nxp.com, michal.vokac@ysoft.com,
l.majewski@majess.pl, linux-pwm@vger.kernel.org,
kernel@pengutronix.de, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/3] pwm: imx27: fix disable state for inverted PWMs
Date: Mon, 21 Sep 2020 11:09:55 +0200 [thread overview]
Message-ID: <20200921090955.sw3mrlxgh45pcpru@pengutronix.de> (raw)
In-Reply-To: <20200909130739.26717-4-m.felsch@pengutronix.de>
[-- Attachment #1: Type: text/plain, Size: 1446 bytes --]
Hello Marco,
On Wed, Sep 09, 2020 at 03:07:39PM +0200, Marco Felsch wrote:
> Up to now disabling the PWM is done using the PWMCR.EN register bit.
> Setting this bit to zero results in the output pin driving a low value
> independent of the polarity setting (PWMCR.POUTC).
>
> There is only little documentation about expectations and requirements
> in the PWM framework but the usual expectation seems to be that
> disabling a PWM or setting .duty_cycle = 0 results in the output driving
s/or/together with/
> the inactive level. The pwm-bl driver for example uses this setting to
> disable the backlight and with the pwm-imx27 driver this results in an
> enabled backlight if the pwm signal is inverted.
>
> Keep the PWMCR.EN bit always enabled and simulate a disabled PWM using
> duty_cycle = 0 to fix this. Furthermore we have to drop the sw-reset
> from apply() else the PWMCR.EN is cleared too. Therefore the
s/else/otherwise/
> pwm_imx27_wait_fifo_slot() is extended to guarantee a free FIFO slot.
>
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Without having looked deeper into this patch the approach described here
looks sound to me. Dropping the sw-reset in .apply is also nice as this
results in a spike.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Marco Felsch <m.felsch@pengutronix.de>
Cc: linux-pwm@vger.kernel.org, michal.vokac@ysoft.com,
kernel@pengutronix.de, Anson.Huang@nxp.com, lee.jones@linaro.org,
s.hauer@pengutronix.de, thierry.reding@gmail.com,
linux-imx@nxp.com, festevam@gmail.com, shawnguo@kernel.org,
l.majewski@majess.pl, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/3] pwm: imx27: fix disable state for inverted PWMs
Date: Mon, 21 Sep 2020 11:09:55 +0200 [thread overview]
Message-ID: <20200921090955.sw3mrlxgh45pcpru@pengutronix.de> (raw)
In-Reply-To: <20200909130739.26717-4-m.felsch@pengutronix.de>
[-- Attachment #1.1: Type: text/plain, Size: 1446 bytes --]
Hello Marco,
On Wed, Sep 09, 2020 at 03:07:39PM +0200, Marco Felsch wrote:
> Up to now disabling the PWM is done using the PWMCR.EN register bit.
> Setting this bit to zero results in the output pin driving a low value
> independent of the polarity setting (PWMCR.POUTC).
>
> There is only little documentation about expectations and requirements
> in the PWM framework but the usual expectation seems to be that
> disabling a PWM or setting .duty_cycle = 0 results in the output driving
s/or/together with/
> the inactive level. The pwm-bl driver for example uses this setting to
> disable the backlight and with the pwm-imx27 driver this results in an
> enabled backlight if the pwm signal is inverted.
>
> Keep the PWMCR.EN bit always enabled and simulate a disabled PWM using
> duty_cycle = 0 to fix this. Furthermore we have to drop the sw-reset
> from apply() else the PWMCR.EN is cleared too. Therefore the
s/else/otherwise/
> pwm_imx27_wait_fifo_slot() is extended to guarantee a free FIFO slot.
>
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Without having looked deeper into this patch the approach described here
looks sound to me. Dropping the sw-reset in .apply is also nice as this
results in a spike.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
[-- Attachment #2: Type: text/plain, Size: 176 bytes --]
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-09-21 9:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-09 13:07 [PATCH 0/3] PWM i.MX27 fix disabled state for inverted signals Marco Felsch
2020-09-09 13:07 ` Marco Felsch
2020-09-09 13:07 ` [PATCH 1/3] pwm: imx27: track clock enable/disable to simplify code Marco Felsch
2020-09-09 13:07 ` Marco Felsch
2020-09-21 8:54 ` Uwe Kleine-König
2020-09-21 8:54 ` Uwe Kleine-König
2020-09-09 13:07 ` [PATCH 2/3] pwm: imx27: move static pwmcr values into probe() function Marco Felsch
2020-09-09 13:07 ` Marco Felsch
2020-09-21 9:01 ` Uwe Kleine-König
2020-09-21 9:01 ` Uwe Kleine-König
2020-09-09 13:07 ` [PATCH 3/3] pwm: imx27: fix disable state for inverted PWMs Marco Felsch
2020-09-09 13:07 ` Marco Felsch
2020-09-21 9:09 ` Uwe Kleine-König [this message]
2020-09-21 9:09 ` Uwe Kleine-König
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=20200921090955.sw3mrlxgh45pcpru@pengutronix.de \
--to=u.kleine-koenig@pengutronix.de \
--cc=Anson.Huang@nxp.com \
--cc=festevam@gmail.com \
--cc=kernel@pengutronix.de \
--cc=l.majewski@majess.pl \
--cc=lee.jones@linaro.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-imx@nxp.com \
--cc=linux-pwm@vger.kernel.org \
--cc=m.felsch@pengutronix.de \
--cc=michal.vokac@ysoft.com \
--cc=s.hauer@pengutronix.de \
--cc=shawnguo@kernel.org \
--cc=thierry.reding@gmail.com \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.