RE: Enable buttons GPIO passthrough

From: "Wang, Kuiying" <kuiying.wang@intel.com>
To: Linus Walleij <linus.walleij@linaro.org>, Joel Stanley <joel@jms.id.au>
Cc: Andrew Jeffery <andrew@aj.id.au>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Andrew Geissler <geissonator@gmail.com>,
	OpenBMC Maillist <openbmc@lists.ozlabs.org>,
	"Mauery, Vernon" <vernon.mauery@intel.com>,
	"Feist, James" <james.feist@intel.com>,
	"Yoo, Jae Hyun" <jae.hyun.yoo@intel.com>,
	"Nguyen, Hai V" <hai.v.nguyen@intel.com>,
	"Khetan, Sharad" <sharad.khetan@intel.com>
Subject: RE: Enable buttons GPIO passthrough
Date: Wed, 16 Jan 2019 14:30:12 +0000	[thread overview]
Message-ID: <959CAFA1E282D14FB901BE9A7BF4E7724E43DAA1@shsmsx102.ccr.corp.intel.com> (raw)
In-Reply-To: <CACRpkdazF1GkXcMK3_S_=cmpj086LckjskkDuE9R+FzWPPCmeQ@mail.gmail.com>

Hi Joel,
Do agree to use proposal #1? (extend "passthrough" to the "direction" property of gpio, use  "value" to control it be disabled/enabled.)

All,
Any other comments?

Thanks,
Kwin.

-----Original Message-----
From: Linus Walleij [mailto:linus.walleij@linaro.org] 
Sent: Tuesday, January 15, 2019 8:10 PM
To: Wang, Kuiying <kuiying.wang@intel.com>
Cc: Andrew Jeffery <andrew@aj.id.au>; Thomas Petazzoni <thomas.petazzoni@bootlin.com>; Joel Stanley <joel@jms.id.au>; open list:GPIO SUBSYSTEM <linux-gpio@vger.kernel.org>; Andrew Geissler <geissonator@gmail.com>; OpenBMC Maillist <openbmc@lists.ozlabs.org>; Mauery, Vernon <vernon.mauery@intel.com>; Feist, James <james.feist@intel.com>; Yoo, Jae Hyun <jae.hyun.yoo@intel.com>
Subject: Re: Enable buttons GPIO passthrough

Hi Kwin,

> Based on pinmux to do passthrough is too complex and no reference,

Don't let that discourage you! We are some of the world's most important software engineers in the kernel, and we don't just do the simple stuff, like filling in the blanks guided by previous example, we do the really complicated stuff of inventing the frameworks.

> I have another 2 simple proposals to do button GPIO passthrough as following:
> 1. extend "passthrough" to the "direction" property of gpio, use 
> "value" to control it be disabled/enabled.

This is what I described in my first reply. A .set_config() option.
But it still needs to patch the DT bindings for generic pin config and add a globally uniquie enumerator for this config to pinconf-generic.h since GPIO is reusing these generics, so begin with that in any case.

> 2. extend "value" property of gpio to support the third value "2", 
> which means pass-through is enabled, otherwise passthrough is disabled.

No, sorry, this is the wrong idea.

.set_value() sets the GPIO line as high or low, it is essentially boolean and it is an integer only for historical reasons.

.set_config() is what we use to set up debounce or open drain and such electronic configurations on GPIO lines, and this should be done there, unless Andrew prefers that it is gets done in the pin control driver.

Yours,
Linus Walleij