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

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Date:	Wed, 28 Aug 2013 11:10:19 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org,
	Christian Ruppert <christian.ruppert@...lis.com>,
	Shinya Kuribayashi <skuribay@...ox.com>,
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v2 1/2] i2c-designware: make HCNT/LCNT values configurable

On Mon, Aug 19, 2013 at 03:07:53PM +0300, 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>

Applied to for-next, thanks!


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