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

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Date:	Sun, 26 Aug 2012 21:33:56 -0700
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 08/25/2012 08:53 AM, Sebastian Hesselbarth wrote:
> On 08/24/2012 05:34 AM, Stephen Warren wrote:
>> On 08/23/2012 05:01 PM, Sebastian Hesselbarth wrote:
>>> 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;
>>>  [...]
>> 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.
>>
>> 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.
> 
> Stephen,
> 
> now I do understand but in the current driver we pass pingroups associated
> with the available functions, i.e. "mpp2" with "uart1", "uart2",
> "sdio0", aso.
> IMHO for the above three functions it would be better to have functions
> associated
> with the corresponding groups, i.e. "uart1" with "mpp_uart1", "mpp2",
> "mpp3", aso.

The pinctrl subsystem does expect a list of functions, and for each
function, a list of the groups where it can be selected. I admit that
when I think about this, it's slightly backward, since HW typically has
a list of pins/groups, and for each, a certain set of functions can be
selected. Oh well...
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