linux-kernel - Re: Fwd: [PATCH 1/3] i2c: Add Device Tree support to the Nomadik I2C driver

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Message-ID: <CACRpkdZ7ESKhokk8Z+6sC9Kq+jPztFNwzger0Db7nCD1fPnG1A@mail.gmail.com>
Date:	Sun, 17 Jun 2012 19:43:13 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Srinidhi Kasagar <srinidhi.kasagar@...ricsson.com>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: Re: Fwd: [PATCH 1/3] i2c: Add Device Tree support to the Nomadik I2C driver

Gah, what a thread...

On Fri, Jun 15, 2012 at 3:18 PM, Lee Jones <lee.jones@...aro.org> wrote:
> On 15/06/12 14:05, Srinidhi Kasagar wrote:
>> On Fri, Jun 15, 2012 at 14:45:11 +0200, Lee Jones wrote:
>>> On 15/06/12 12:50, Srinidhi Kasagar wrote:

>>>>> +static struct nmk_i2c_controller u8500_i2c = {
>>>>> +       /*
>>>>> +        * Slave data setup time; 250ns, 100ns, and 10ns, which
>>>>> +        * is 14, 6 and 2 respectively for a 48Mhz i2c clock.
>>>>> +        */
>>>>> +       .slsu           = 0xe,
>>>>> +       .tft            = 1,      /* Tx FIFO threshold */
>>>>> +       .rft            = 8,      /* Rx FIFO threshold */
>>>>> +       .clk_freq       = 100000, /* std. mode operation */
>>>>> +       .timeout        = 200,    /* Slave response timeout(ms) */
>>>>> +       .sm             = I2C_FREQ_MODE_FAST,
>>>>
>>>> How is this possible? you are setting clk_freq as 100kb/s and mode
>>>> as fast mode which is supposed to be 400kb/s.
>>>
>>> That's not how I read it:
>>
>>
>> But it is not readable. It confuses people.
>
> I understood it. :)
>
> If you think it's unclear speak to the author, Linus. He's CC'ed.

Author of what? The i2c driver was written by Srinidhi. (The
MODULE_AUTHOR() clause should be a good hint...)

But it's true that board data for the ux500 kernel use
100000 Hz and I2C_FREQ_MODE_FAST, in the board-mop500.c
file, like this:

U8500_I2C_CONTROLLER(0, 0xe, 1, 8, 100000, 200, I2C_FREQ_MODE_FAST);
U8500_I2C_CONTROLLER(1, 0xe, 1, 8, 100000, 200, I2C_FREQ_MODE_FAST);
U8500_I2C_CONTROLLER(2, 0xe, 1, 8, 100000, 200, I2C_FREQ_MODE_FAST);
U8500_I2C_CONTROLLER(3, 0xe, 1, 8, 100000, 200, I2C_FREQ_MODE_FAST);

This is indeed a bit odd. But obviously it works... But reading some
fixes in another tree it seems it should look like this:

/*
 * The board uses 4 i2c controllers, initialize all of
 * them with slave data setup time of 250 ns,
 * Tx & Rx FIFO threshold values as 1 and standard
 * mode of operation
 */
U8500_I2C_CONTROLLER(0, 0xe, 1, 8, 400000, 200, I2C_FREQ_MODE_FAST);
U8500_I2C_CONTROLLER(1, 0xe, 1, 8, 400000, 200, I2C_FREQ_MODE_FAST);
U8500_I2C_CONTROLLER(2, 0xe, 1, 8, 400000, 200, I2C_FREQ_MODE_FAST);
U8500_I2C_CONTROLLER(3, 0xe, 1, 8, 400000, 200, I2C_FREQ_MODE_FAST);

Which makes *much* more sense.

I'll cook a separate patch for this or something.

Thanks,
Linus Walleij
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