linux-kernel - Re: [PATCH] [RFC] pinctrl: add a driver for Energy Micro's efm32 SoCs

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Message-ID: <20111209175327.GQ31337@atomide.com>
Date:	Fri, 9 Dec 2011 09:53:27 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Dong Aisheng <dongas86@...il.com>,
	Shawn Guo <shawn.guo@...escale.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [PATCH] [RFC] pinctrl: add a driver for Energy Micro's efm32
 SoCs

* Tony Lindgren <tony@...mide.com> [111209 08:53]:
> * Stephen Warren <swarren@...dia.com> [111209 08:17]:
> > Dong Aisheng wrote at Friday, December 09, 2011 8:03 AM:
> > ...
> > > I agree that parsing data from device tree increases much effort
> > > because we can not using any help functions like microes in dts file and we have
> > > to construct the structure we need in driver by parsing that data.
> > > And it will increase dtsi file's size a lot when after adding all functions.
> > > 
> > > I wonder if we can define that data as a pdata in a .c file and only
> > > get a pointer from dts file. That would make life much easier.
> > 
> > You can't get pointers themselves directly from a .dts file, since the
> > .dts file author has no idea what the memory layout (or even which OS)
> > is present on the running system.
> > 
> > An alternative is to key off the compatible flag in the device tree,
> > and use that to index a table that points at the various structures you
> > want pointers to.
> > 
> > struct of_device_id's .data field, and the function of_match_device()
> > are for exactly that purpose; see the way the Tegra pinctrl driver that
> > I posted uses them for an example of mapping compatible flag to per-
> > SoC initialization function pointers.
> 
> For letting a device do it's pingroup in DT, I've played with the
> following:
> 
> 	/*      mux func phandle mux func name    hw initial flags */
> 	pins = <&uart3_rx_irrx>, "uart3_rx_irrx", <0xdeadbeef>,
> 		<&uart3_tx_irtx>, "uart3_tx_irtx", <0xdeadbeef>;
> 
> But it seems that doing mixed-property arrays gets nasty as any
> data after a string has a high likelihood of getting misaligned
> since a mixed-property array is a string array with the string
> embedded in it with the registers. That leads into nasty string
> parsing that can be extremely flakey with buggy DT data. So it
> seems that using a string there is only safe as the last element,
> which means we can't use names for multiple pins.
> 
> So I've pretty much come to the conclusion that we would have to
> use something like this instead:
> 
> 	/*      phandle        f hw specific initial flags */
> 	pins = <&uart3_rx_irrx 0 0xdeadbeef
> 		&uart3_tx_irtx 0 0xdeadbeef>;
> 
> This however has a problem for cases where we may not have a phandle
> in DT for the mux function. For example, let's assume that we'll have
> tens of thousands of lines of mux data for omaps (we already have
> over 6k LOC) and just want to load that from /lib/firmware to avoid
> bloating the kernel. In that case we won't have the phandle for the
> mux function in DT.
> 
> It would be _really_nice_ to use DT in the missing phandle case also
> for doing the device to mux function mapping based on a function name
> when no phandle is available.
> 
> But so far I have not found a good way of doing both phandle and
> optional name type thing. Anybody got some good ideas for that?

Oh forgot to mention of course what Benoit came up which is reg-names.
That of course is doable with both phandles and pin names:

So optionally either

	pins = <&uart3_rx_irrx &uart3_tx_irtx>;
or

	pin-names = "uart3_rx_irrx",  "uart3_tx_irtx";

and both pins and pin-names could have optional hardware specific
board default flags:

	pin-flags = <0xdeadbeef 0xdeadbeef>;

The pin-flags could end up being defines if dtc will at some point
support preprocessing the .dtc files.
 
> BTW, this same problem applies also to clock framwork where we may
> have multiple sources of clocks to register and map to devices.

Regards,

Tony
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