linux-kernel - RE: [PATCH 20/20] pinctrl: Enhance mapping table to support pin config operations

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Date:	Mon, 27 Feb 2012 11:02:01 -0800
From:	Stephen Warren <swarren@...dia.com>
To:	Dong Aisheng <aisheng.dong@...escale.com>
CC:	Linus Walleij <linus.walleij@...ricsson.com>,
	"B29396@...escale.com" <B29396@...escale.com>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"dongas86@...il.com" <dongas86@...il.com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"thomas.abraham@...aro.org" <thomas.abraham@...aro.org>,
	"tony@...mide.com" <tony@...mide.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 20/20] pinctrl: Enhance mapping table to support pin
 config operations

Dong Aisheng wrote at Monday, February 27, 2012 5:21 AM:
> On Sun, Feb 19, 2012 at 11:46:00PM -0700, Stephen Warren wrote:
> > The pinctrl mapping table can now contain entries to:
> > * Set the mux function of a pin group
> > * Apply a set of pin config options to a pin or a group
> >
> > This allows pinctrl_select_state() to apply pin configs settings as well
> > as mux settings.
> >
> > Signed-off-by: Stephen Warren <swarren@...dia.com>
...
> > +The mapping table may also contain pin configuration entries. It's common for
> > +each pin/group to have a number of configuration entries that affect it, so
> > +the table entries for configuration reference an array of config parameters
> > +and values. An example using the convenience macros is shown below:
> > +
> > +static unsigned long i2c_grp_configs[] = {
> > +	FOO_PIN_DRIVEN,
> > +	FOO_PIN_PULLUP,
> > +};
> > +
> > +static unsigned long i2c_pin_configs[] = {
> > +	FOO_OPEN_COLLECTOR,
> > +	FOO_SLEW_RATE_SLOW,
> > +};
> > +
> > +static struct pinctrl_map __initdata mapping[] = {
> > +	PIN_MAP_MUX_GROUP("foo-i2c.0", "default", "pinctrl-foo", "i2c0", "i2c0"),
> > +	PIN_MAP_MUX_CONFIGS_GROUP("foo-i2c.0", "default", "pinctrl-foo", "i2c0", i2c_grp_configs),
> > +	PIN_MAP_MUX_CONFIGS_PIN("foo-i2c.0", "default", "pinctrl-foo", "i2c0scl", i2c_pin_configs),
> > +	PIN_MAP_MUX_CONFIGS_PIN("foo-i2c.0", "default", "pinctrl-foo", "i2c0sda", i2c_pin_configs),
>
> I still have not read all over this patch.
> But one question i'm considering is that
> will this way here also work for "virtual" group?
> For example, the virtual group "i2c_grp_configs" may actually contains
> the config for each pin in that group?
> The core will handle this difference or let each driver to handle it?

Since the core has no knowledge of virtual groups, everything has to be
handled inside the pin controller driver: When the core asks the driver
to enumerate the groups it supports, those virtual groups must be included
in the list. The mapping table may contain entries to configure those
virtual groups, which will be passed on to the driver to implement as it
sees fit. So, in short, yes, I believe this handles virtual groups just
fine.

> > @@ -1022,7 +1074,7 @@ Since it may be common to request the core to hog a few always-applicable
> >  mux settings on the primary pin controller, there is a convenience macro for
> >  this:
> >
> > -PIN_MAP_SYS_HOG("active", "pinctrl-foo", "power_func")
>
> Hmm?
> Why remove this one?

In the patch I posted, I simplified the mapping table macros by replacing
all mux entries with a single macro PIN_MAP_MUX_GROUP(). However, I've
since modified the patch to include a number of special-case macros, so
this macro has been added back (albeit under a slightly different name).

> > +int pinctrl_get_pin_id(struct pinctrl_dev *pctldev,
> > +		       const char *pin)
> > +{
> > +	unsigned int i;
> > +
> > +	for (i = 0; i < pctldev->desc->npins; i++) {
> > +		if (pctldev->desc->pins[i].name == NULL)
> > +			continue;
> > +		if (!strcmp(pin, pctldev->desc->pins[i].name)) {
> > +			dev_dbg(pctldev->dev, "found pin id %u for %s\n",
> > +				i, pin);
> > +			return i;
>
> It looks actually this is not a PIN id.
> It's just the index of the pin array.
> Pin has its own id:
> struct pinctrl_pin_desc {
> 	unsigned number;
> 	const char *name;
> };

I guess I should just delete this function and call pin_get_from_name()
instead.

However, this does raise one question:

Right now, pin_config_set() calls pin_get_from_name() to find the pin
ID of a pin. This returns that "number" field in the struct above. This
is then passed to the pin controller driver's pin_config_set() callback.
Hence, the pin ID value passed to pin_config_set() can't be used to index
into the driver's own pin_desc array if the pin numbers are sparse. Is
that intended? I suppose it's OK since any driver-specific information
about each pin can't be stored in the pin_desc array anyway, since that
array has a standard type without space for driver-specific data, and
any driver-specific array would probably be indexed by the values in the
.number field, not the pin_desc array index.

Thanks.

-- 
nvpublic

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