linux-kernel - Re: [PATCH 09/14] i2c: Add Device Tree support to the Nomadik I2C driver

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Date:	Mon, 11 Jun 2012 22:37:14 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linus.walleij@...ricsson.com, arnd@...db.de,
	grant.likely@...retlab.ca, linux-i2c@...r.kernel.org
Subject: Re: [PATCH 09/14] i2c: Add Device Tree support to the Nomadik I2C driver

On Mon, Jun 11, 2012 at 5:25 PM, Lee Jones <lee.jones@...aro.org> wrote:

> As new users are
> added, it is expected that they will be Device Tree compliant.
> If this is the case, we will look up their initialisation values
> by compatible entry, then apply them forthwith.
(...)
> +static struct nmk_i2c_controller u8500_i2c = {
> +       /*
> +        * slave data setup time, which is
> +        * 250 ns,100ns,10ns which is 14,6,2
> +        * respectively for a 48 Mhz
> +        * i2c clock
> +        */
> +       .slsu           = 0xe,
> +       /* Tx FIFO threshold */
> +       .tft            = 1,
> +       /* Rx FIFO threshold */
> +       .rft            = 8,
> +       /* std. mode operation */
> +       .clk_freq       = 100000,
> +       /* Slave response timeout(ms) */
> +       .timeout        = 200,
> +       .sm             = I2C_FREQ_MODE_FAST,
> +};

So why don't we create proper device tree bindings for the above platform
data?

For example several driver under
Documentation/devicetree/bindings/i2c/*
define the .clk_freq above as "clock-frequency"

samsung-i2c even has this:
samsung,i2c-sda-delay = <100>;
samsung,i2c-max-bus-freq = <100000>;

Where i2c-sda-delay corresponds to slsu above.

I suspect .sm can be derived from the frequency so it
is "FAST" whenever the frequency > 100000.

This looks to me like a way to push the burden of doing the real
device tree binding for the above to the next user.
(Which will likely be me, so therefore I care a bit ...)

Yours,
Linus Walleij
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