linux-kernel - Re: [PATCH 2/2] pinctrl: add a generic control interface

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Date:	Sun, 23 Oct 2011 16:25:41 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Stephen Warren <swarren@...dia.com>
CC:	Linus Walleij <linus.walleij@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Barry Song <21cnbao@...il.com>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	David Brown <davidb@...eaurora.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 2/2] pinctrl: add a generic control interface

On Thu, Oct 20, 2011 at 10:26:43AM -0700, Stephen Warren wrote:
> Shawn Guo wrote at Wednesday, October 19, 2011 8:32 PM:
> > On Wed, Oct 19, 2011 at 06:21:14PM +0200, Linus Walleij wrote:
> ...
> > > +int pin_config_group(struct pinctrl_dev *pctldev, const char *pin_group,
> > > +		     enum pin_config_param param, unsigned long data)
> ...
> > > +enum pin_config_param {
> > > +	PIN_CONFIG_BIAS_UNKNOWN,
> > > +	PIN_CONFIG_BIAS_FLOAT,
> > > +	PIN_CONFIG_BIAS_HIGH_IMPEDANCE,
> > > +	PIN_CONFIG_BIAS_PULL_UP,
> > > +	PIN_CONFIG_BIAS_PULL_DOWN,
> > > +	PIN_CONFIG_BIAS_HIGH,
> > > +	PIN_CONFIG_BIAS_GROUND,
> > > +	PIN_CONFIG_DRIVE_UNKNOWN,
> > > +	PIN_CONFIG_DRIVE_PUSH_PULL,
> > > +	PIN_CONFIG_DRIVE_OPEN_DRAIN,
> > > +	PIN_CONFIG_DRIVE_OPEN_SOURCE,
> > > +	PIN_CONFIG_DRIVE_OFF,
> > > +	PIN_CONFIG_INPUT_SCHMITT,
> > > +	PIN_CONFIG_SLEW_RATE_RISING,
> > > +	PIN_CONFIG_SLEW_RATE_FALLING,
> > > +	PIN_CONFIG_LOAD_CAPACITANCE,
> > > +	PIN_CONFIG_WAKEUP_ENABLE,
> > > +	PIN_CONFIG_END,
> > > +};
> > 
> > IMO, trying to enumerate all possible pin_config options is just to
> > make everyone's life harder.  Firstly, this enumeration is far from
> > completion, for imx6 iomuxc example, we have 3 options for pull-up,
> > 22, 47 and 100 kOhm, and 7 options for driver-strength, 34, 40, 48,
> > 60, 80, 120, and 240 Ohm.  It's just so hard to make this enumeration
> > complete.  Secondly, defining this param as enum requires the API
> > user to call the function multiple times to configure one pin.  For
> > example, if I want to configure pin_foo as slow-slew, open-drain,
> > 100 kOhm pull-up and 120 Ohm driver-strength, I will have to call
> > pin_config(pctldev, pin_foo, ...) 4 times to achieve that.
> > 
> > I like Stephen's idea about having 'u32 param' and let pinctrl drivers
> > to encode/decode this u32 for their pinctrl controller.  It makes
> > people's life much easier.
> 
> That's not quite what I meant.
> 
> I meant that I thought the types for param and value should be simple
> integers, with meanings of the values defined by the individual drivers,
> rather than a system-defined enum.
> 
> However, I wasn't envisaging packing multiple fields into the "value"
> parameter; that would essentially be packing a struct into a u32 for
> transport. I still figured that "param" would logically be an enum,
> and represent a single modifiable parameter, and "data"/"value" would
> be the single value of that one parameter.
> 
Oops, I misread your idea.  Reading it correctly, I do not like it
either :)  It does not resolve my concern that we need to call the API
multiple times to configure one pin.

> Still, perhaps packing stuff is an option that makes sense in some cases,

I feel strongly that this is what we want.

> depending on what API we end up with to manipulate the parameters, and
> where the source of "data"/"value" is (encoded into client driver, or
> from some hidden table passed to pinmux core by board, with the values
> being passed directly to the pinmux drivers without the client drivers
> seeing them)

I do not think client drivers care about the parameters.  For the mmc
example I put earlier, all it needs from pinctrl subsystem is "Hey,
I'm going to switch bus clock to a higher frequency 100 MHz, please
configure mmc pins properly for that."

-- 
Regards,
Shawn

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