linux-kernel - Re: [PATCH 1/4 v4] drivers: create a pin control subsystem

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Date:	Thu, 25 Aug 2011 13:58:12 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Stephen Warren <swarren@...dia.com>,
	Linus Walleij <linus.walleij@...ricsson.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>,
	Lee Jones <lee.jones@...aro.org>,
	Joe Perches <joe@...ches.com>,
	Russell King <linux@....linux.org.uk>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	ext Tony Lindgren <tony@...mide.com>,
	David Brown <davidb@...eaurora.org>,
	Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [PATCH 1/4 v4] drivers: create a pin control subsystem

On Thu, Aug 25, 2011 at 1:04 PM, Sascha Hauer <s.hauer@...gutronix.de> wrote:

> Not really. UART2_CTS can't be routed to arbitrary pads, but it can be
> routed to more than one pad:
>
> #define _MX51_PAD_EIM_D16__UART2_CTS            IOMUX_PAD(0x3f0, 0x5c, 3, 0x0000, 0, 0)
> #define _MX51_PAD_EIM_D25__UART2_CTS            IOMUX_PAD(0x414, 0x80, 4, 0x0000, 0, 0)
> #define _MX51_PAD_USBH1_DATA0__UART2_CTS        IOMUX_PAD(0x688, 0x288, 1, 0x0000, 0, 0)

Aha!

Is it typically a few pads like this, say 2,3,4 alternatives,
sometimes just one?

So the actual relation is not 1..1 nor 1...* but 1..<a few>?

> This is why there can't be a setup_iomux(uart2) function without
> being able to specify *which* pads in a board specific way.

In the current design it is the pinmux driver that
keeps track of that. Not the subsystem.

I think the question then is how the pinctrl subsystem
can help out in keeping that information together.

I'll try to think of something ...

Thanks,
Linus Walleij
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