linux-kernel - Re: pinctrl_config APIs, and other pinmux questions

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Message-ID: <20111019031446.GA31162@S2100-06.ap.freescale.net>
Date:	Wed, 19 Oct 2011 11:14:47 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Stephen Warren <swarren@...dia.com>
CC:	Linus Walleij <linus.walleij@...ricsson.com>,
	Lee Jones <lee.jones@...aro.org>,
	Joe Perches <joe@...ches.com>,
	Russell King <linux@....linux.org.uk>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	David Brown <davidb@...eaurora.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Stijn Devriendt <highguy@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Barry Song <21cnbao@...il.com>
Subject: Re: pinctrl_config APIs, and other pinmux questions

On Mon, Oct 17, 2011 at 08:51:11AM -0700, Stephen Warren wrote:
> Shawn Guo wrote at Friday, October 14, 2011 9:12 PM:
> > On Fri, Oct 14, 2011 at 08:53:33AM -0700, Stephen Warren wrote:
> ...
> > > Having the driver expose a list of all possible combinations of pin
> > > configurations seems impractical, for the same reason as I objected to
> > > the original proposal for how the driver listed functions; there are
> > > simply far too many pin config parameters and legal value to list the
> > > entire set of combinations.
> > >
> > I did not mean to list the entire set of combinations.  For given
> > function, the applicable number of config should be very limited.
> > For most cases, it could be just one.  For imx6q usdhc example, it's
> > 3, for 50M, 100M and 200M SD bus clock cases.
> 
> Shawn,
> 
> Are you talking about entries in the (board-specific) mapping table, which
> I agree would contain the useful subset of combinations of options, or a
> list of possible settings exposed by the SoC driver, which would have to
> expose all possibilities, or they wouldn't be available for the mapping
> table to select from?
> 
> In the case of "a list of possible settings exposed by the SoC driver",
> 
> * If such a list (of combinations) were to exist, I think it'd need to
> include all combinations (the cross-product of all individual config
> params) in general.
> 
> * I can certainly imagine that for some SoCs, or for a particular device
> on a SoC, or for a particular board, only a subset of those would be useful,
> and hence a limited set would be useful. However, that selection is up to
> the board mapping table not the SoC driver in general.
> 
> * In Tegra's case at least, I think a number of the numeric values (e.g.
> pull strength with range 0..31) may be for board calibration, and besides
> that, most combinations of param values would be useful in some case, and
> hence we'd always have to expose everything, in order to allow the board
> mapping table to be able to pick anything the designer needed.
> 
> * As such, I think the SoC driver should at most list the legal range for
> each param individually, and let the board-specific mapping table choose
> the combination(s) required.
> 
Yes, I meant the list of settings exposed by pinctrl driver.  But it
seems that in your case you need to list all the possible combinations
of pin configurations.  Then I agree it's impractical to have pinctrl
driver to maintain this list.

-- 
Regards,
Shawn

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