From: Greg KH <gregkh@linuxfoundation.org>
To: Douglas Anderson <dianders@chromium.org>
Cc: Linus Walleij <linus.walleij@linaro.org>,
Heiko Stuebner <heiko@sntech.de>,
Caesar Wang <wxt@rock-chips.com>,
Chris Zhong <zyw@rock-chips.com>,
linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org
Subject: Re: [PATCH v3] drivers/pinctrl: Add the concept of an "init" state
Date: Tue, 20 Oct 2015 22:06:41 -0700 [thread overview]
Message-ID: <20151021050641.GA5198@kroah.com> (raw)
In-Reply-To: <1445400906-32284-1-git-send-email-dianders@chromium.org>
On Tue, Oct 20, 2015 at 09:15:06PM -0700, Douglas Anderson wrote:
> For pinctrl the "default" state is applied to pins before the driver's
> probe function is called. This is normally a sensible thing to do,
> but in some cases can cause problems. That's because the pins will
> change state before the driver is given a chance to program how those
> pins should behave.
>
> As an example you might have a regulator that is controlled by a PWM
> (output high = high voltage, output low = low voltage). The firmware
> might leave this pin as driven high. If we allow the driver core to
> reconfigure this pin as a PWM pin before the PWM's probe function runs
> then you might end up running at too low of a voltage while we probe.
>
> Let's introudce a new "init" state. If this is defined we'll set
> pinctrl to this state before probe and then "default" after probe
> (unless the driver explicitly changed states already).
>
> An alternative idea that was thought of was to use the pre-existing
> "sleep" or "idle" states and add a boolean property that we should
> start in that mode. This was not done because the "init" state is
> needed for correctness and those other states are only present (and
> only transitioned in to and out of) when (optional) power management
> is enabled.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Tested-by: Caesar Wang <wxt@rock-chips.com>
> ---
> Changes in v3:
> - Moved declarations to pinctrl/devinfo.h
> - Fixed author/SoB
>
> Changes in v2:
> - Added comment to pinctrl_init_done() as per Linus W.
>
> As mentioned in v2 repost, reposted after 1 year of no activity since
> Caesar Wang found a use for this. See
> <https://patchwork.kernel.org/patch/7444161/>. I hope it's OK that I
> left Greg KH's Ack...
The ack from me is fine.
thanks,
greg k-h
next prev parent reply other threads:[~2015-10-21 5:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-21 4:15 [PATCH v3] drivers/pinctrl: Add the concept of an "init" state Douglas Anderson
2015-10-21 5:06 ` Greg KH [this message]
2015-10-27 10:25 ` Linus Walleij
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=20151021050641.GA5198@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=dianders@chromium.org \
--cc=heiko@sntech.de \
--cc=linus.walleij@linaro.org \
--cc=linux-gpio@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=wxt@rock-chips.com \
--cc=zyw@rock-chips.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).