linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Guenter Roeck <linux@roeck-us.net>
To: Thierry Reding <thierry.reding@gmail.com>
Cc: Jean Delvare <jdelvare@suse.com>, Kamil Debski <kamil@wypas.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] hwmon: pwm-fan: Set fan speed to 0 on suspend
Date: Fri, 21 Sep 2018 06:23:54 -0700	[thread overview]
Message-ID: <20180921132354.GA16764@roeck-us.net> (raw)
In-Reply-To: <20180921101048.11679-2-thierry.reding@gmail.com>

On Fri, Sep 21, 2018 at 12:10:48PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> Technically this is not required because disabling the PWM should be
> enough. However, when support for atomic operations was implemented in
> the PWM subsystem, only actual changes to the PWM channel are applied
> during pwm_config(), which means that during after resume from suspend
> the old settings won't be applied.
> 
> One possible solution is for the PWM driver to implement its own PM
> operations such that settings from before suspend get applied on resume.
> This has the disadvantage of completely ignoring any particular ordering
> requirements that PWM user drivers might have, so it is best to leave it
> up to the user drivers to apply the settings that they want at the
> appropriate time.
> 
> Another way to solve this would be to read back the current state of the
> PWM at the time of resume. That way, in case the configuration was lost
> during suspend, applying the old settings in PWM user drivers would
> actually get them applied because they differ from the current settings.
> However, not all PWM drivers support reading the hardware state, and not
> all hardware may support it.
> 
> The best workaround at this point seems to be to let PWM user drivers
> tell the PWM subsystem that the PWM is turned off by, in addition to
> disabling it, also setting the duty cycle to 0. This causes the resume
> operation to apply a configuration that is different from the current
> configuration, resulting in the proper state from before suspend getting
> restored.
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>

Applied.

Thanks,
Guenter

  reply	other threads:[~2018-09-21 13:23 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-21 10:10 [PATCH 1/2] hwmon: pwm-fan: Silence error on probe deferral Thierry Reding
2018-09-21 10:10 ` [PATCH 2/2] hwmon: pwm-fan: Set fan speed to 0 on suspend Thierry Reding
2018-09-21 13:23   ` Guenter Roeck [this message]
2018-09-21 13:21 ` [PATCH 1/2] hwmon: pwm-fan: Silence error on probe deferral Guenter Roeck

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=20180921132354.GA16764@roeck-us.net \
    --to=linux@roeck-us.net \
    --cc=b.zolnierkie@samsung.com \
    --cc=jdelvare@suse.com \
    --cc=kamil@wypas.org \
    --cc=linux-hwmon@vger.kernel.org \
    --cc=linux-kernel@vger.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 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).