linux-kernel - Re: Pinmux bindings proposal V2

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Date:	Mon, 30 Jan 2012 11:13:48 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Simon Glass <sjg@...omium.org>
Cc:	Tony Lindgren <tony@...mide.com>,
	Stephen Warren <swarren@...dia.com>,
	Dong Aisheng-B29396 <B29396@...escale.com>,
	"Linus Walleij (linus.walleij@...aro.org)" <linus.walleij@...aro.org>,
	"Sascha Hauer (s.hauer@...gutronix.de)" <s.hauer@...gutronix.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	Dong Aisheng <dongas86@...il.com>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	"Grant Likely (grant.likely@...retlab.ca)" 
	<grant.likely@...retlab.ca>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Pinmux bindings proposal V2

On Fri, Jan 27, 2012 at 07:43:36AM -0800, Simon Glass wrote:
...
> The cost of the pmx@dta node is about 12 bytes for the header (it
> depends on the length of the name), and each of the properties above
> is 16 bytes. So in total this node is 76 bytes. If we have 250 pins
> being muxed as Tegra3 then this is about 20KB (including a bit of
> slack for longer names). My point about being able to 'optimise out'
> some of these remains, though, but probably not for the kernel.
> 
> Stephen's 'mux' property uses 12 bytes plus 8 bytes per pin/group (I
> am removing the prefixes):
> 
>                        mux =
>                                <PG_DTA   MUX_SDIO1>
>                                <PG_DTD   MUX_SDIO1>;
> 
> so 28 bytes. What I proposed would use (12 + 2 * 16) per pin/group, or
> 44 bytes (60% bigger):
> 
It's not only about size but also run-time tree travelling efficiency.
Your proposal requires every single pin show as a node in device tree.
Looking at these for_each_node_by_*() APIs in include/linux/of.h, you
might agree we should avoid bloating device tree with so many nodes.

-- 
Regards,
Shawn
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