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

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Date:   Wed, 31 Aug 2016 00:24:36 +0000
From:   "Lee, Zhuo-hao" <zhuo-hao.lee@...el.com>
To:     Wolfram Sang <wsa@...-dreams.de>
CC:     "jarkko.nikula@...ux.intel.com" <jarkko.nikula@...ux.intel.com>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1] i2c: designware: save the preset value of
 DW_IC_SDA_HOLD

>On Sat, Aug 27, 2016 at 03:39:30PM +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.
>> 
>> Signed-off-by: Zhuo-hao Lee <zhuo-hao.lee@...el.com>

>Looks good. But is it a bugfix? Looks more like for-next material to me, but not sure...
Yes, as least for me, this is a bug.
This is an error handling in case Device Tree, built-in device properties and ACPI were not set 
the SDA hold time. We should use the firmware setting instead of chipset reset value.