linux-kernel - Re: [PATCH] pinctrl: intel: Implements gpio free function

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Date:   Thu, 21 Mar 2019 11:23:30 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     zhuchangchun <zhuchangchun@...e.com>, linus.walleij@...aro.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        hendychu@...yun.com
Subject: Re: [PATCH] pinctrl: intel: Implements gpio free function

On Thu, Mar 21, 2019 at 10:44:20AM +0200, Mika Westerberg wrote:
> On Thu, Mar 21, 2019 at 10:35:24AM +0800, zhuchangchun wrote:
> > When we use the gpio to control some peripheral devices,and try to
> > export the gpio first,then unexport the gpio, we test the signal with
> > oscilloscope,and find the signal can't meet the requirements,because
> > after we unexported the gpio,the gpio's register(tx and rx)value can't
> > be recovered,and this will infruence the device work flow.
> 
> After you unexport GPIO it can go back to any previous mode it was. If
> you need to use it as GPIO then why unexport it in the first place?

...and on top of that GPIO sysfs interface is deprecated.

> > We check the gpio's unexport code work flow, then find the gpio's free
> > hook function has not been implemented, After we add pinmux_ops' free
> > function to set exported gpio to recover its original value,the problem
> > is fixed.
> 
> I don't think this is what ->free callback should do (assuming we decide
> to implement it since we don't implement ->release either). It is
> supposed to reverse effects of ->request which is what it currently does ;-)

Exactly!

-- 
With Best Regards,
Andy Shevchenko