linux-kernel - Re: [PATCH v2 1/2] i2c-designware: make HCNT/LCNT values configurable

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Date:	Mon, 19 Aug 2013 21:40:40 +0900
From:	Shinya Kuribayashi <skuribay@...ox.com>
To:	mika.westerberg@...ux.intel.com
CC:	linux-kernel@...r.kernel.org, wsa@...-dreams.de,
	christian.ruppert@...lis.com, linux-i2c@...r.kernel.org
Subject: Re: [PATCH v2 1/2] i2c-designware: make HCNT/LCNT values configurable

On 8/19/13 9:07 PM, Mika Westerberg wrote:
> The DesignWare I2C controller has high count (HCNT) and low count (LCNT)
> registers for each of the I2C speed modes (standard and fast). These
> registers are programmed based on the input clock speed in the driver.
>
> The current code calculates these values based on the input clock speed and
> tries hard to meet the I2C bus timing requirements. This could result
> non-optimal values with regarding to the bus speed. For example on Intel
> BayTrail we get bus speed of 315.41kHz which is ~20% slower than we would
> expect (400kHz) in fast mode (even though the timing requirements are met).
>
> This patch makes it possible for the platform code to pass more optimal
> HCNT/LCNT values to the core driver if they are known beforehand. If these
> are not set we use the calculated and more conservative values.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

Looks good, thanks.

Acked-by: Shinya Kuribayashi <skuribay@...ox.com>

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