linux-kernel - Re: [PATCH v2 1/9] pinctrl: mvebu: pinctrl driver core

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Date:	Thu, 23 Aug 2012 21:34:41 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
CC:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	Lior Amsalem <alior@...vell.com>, Andrew Lunn <andrew@...n.ch>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/9] pinctrl: mvebu: pinctrl driver core

On 08/23/2012 05:01 PM, Sebastian Hesselbarth wrote:
> On 08/23/2012 11:26 PM, Stephen Warren wrote:
>> As you may have guessed, I strongly prefer the hard-coded static table
>> based approach, or at least separating the definition of known
>> pins/groups/functions from the configuration nodes that define which
>> particular mux settings to actually use.
>>
>> Puting this all a little more simply, the pinctrl core wants to generate
>> a list of all known functions. It is a single global/unified list. It
>> first calls pinmux_ops.get_functions_count() to find out how many
>> functions there are in the list, then pinmux_ops.get_function_name() for
>> each one to find its name, then pinmux_ops.get_function_groups() to find
>> out which groups allow that function to be mux'd onto them.
> 
> Ok, now this becomes a little bit more clear to me.
> 
> Consider uart1 on dove is muxable to:
> mpp2 uart1(rts), mpp3 uart1(cts), mpp21 uart1(rts), mpp22 uart1(cts),
> and finally mpp_uart1(rx and tx).
> 
> So possible, valid combinations for uart1 would be:
> (a) mpp_uart1;
> (b) mpp_uart1, mpp2, mpp3;
> (c) mpp_uart1, mpp21, mpp22;
> (d) mpp_uart1, mpp2, mpp22;
> (e) mpp_uart1, mpp21, mpp3;
> 
> Now what we currently do is, use DT to setup all known functions with e.g.
> marvell,pins = "mpp_uart1", "mpp2", "mpp22" and marvell,function = "uart1".
> This requires to count all pinctrl DT node children to count the known
> functions that can ever be muxed to. It will never allow to mux uart1 to sw
> flow control during run-time when there was no DT child node for it.

In the example above, there is a single function named "uart1". If this
was all the HW supported, I'd expect the driver's
pinmux_ops.get_functions_count() to return 1,
pinmux_ops.get_function_name(0) to return "uart1", and
pinmux_ops.get_function_name(n>0) to return an error.

In practice, I assume there are many other options that can be muxed
onto mpp2/3/21/22/uart1, so they'd be included in the list as well.

> But you are proposing to scan the list passed from SoC specific driver
> for all
> possible marvell,function ("uart1", "uart2", "sdio0", ...) and build up
> lists
> of pingroups that can be used with this specific marvell,function; or
> even build
> up lists of pingroups that allow uart1(rts), and another one for
> uart1(cts), ...?

I don't expect any scanning, no. I'd expect that tables provided by the
SoC-specific drivers to be:

* A table of pins
* A table of groups
* A table of functions

No scanning involved.
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