linux-kernel - Re: [PATCH v1] i2c: designware: save the preset value of DW_IC_SDA

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Message-ID: <70696be2-bead-9241-508d-dd1b02181766@linux.intel.com>
Date:   Mon, 29 Aug 2016 09:17:26 +0300
From:   Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Zhuo-hao Lee <zhuo-hao.lee@...el.com>,
        mika.westerberg@...ux.intel.com, wsa@...-dreams.de,
        linux-i2c@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] i2c: designware: save the preset value of
 DW_IC_SDA_HOLD

On 08/28/2016 03:31 PM, Andy Shevchenko wrote:
> On Sat, 2016-08-27 at 15:39 +0800, Zhuo-hao Lee wrote:
>> There are several ways to set the SDA hold time for i2c controller,
>> including: Device Tree, built-in device properties and ACPI. However,
>> if the SDA hold time is not specified by above method, we should
>> read the value, where it is preset by firmware, and save it to
>> sda_hold_time. This is needed because when i2c controller enters
>> runtime suspend, the DW_IC_SDA_HOLD value will be reset to chipset
>> default value. And during runtime resume, i2c_dw_init will be called
>> to reconfigure i2c controller. If sda_hold_time is zero, the chipset
>> default hold time will be used, that will be too short for some
>> platforms. Therefore, to have a better tolerance, the DW_IC_SDA_HOLD
>> value should be kept by sda_hold_time.
>
> Looks good to me.
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>
Acked-by: Jarkko Nikula <jarkko.nikula@...ux.intel.com>