linux-kernel - Re: [PATCH v2 14/16] mfd: intel-lpss: Pass SDA hold time to I2C host controller driver

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Date:	Mon, 8 Feb 2016 11:09:43 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	linux-i2c@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Kevin Fenzi <kevin@...ye.com>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 14/16] mfd: intel-lpss: Pass SDA hold time to I2C host
 controller driver

On Mon, Nov 30, 2015 at 05:11:42PM +0200, Andy Shevchenko wrote:
> From: Mika Westerberg <mika.westerberg@...ux.intel.com>
> 
> Intel Skylake the LPSS I2C pad circuit has internal delays that require
> programming non-zero SDA hold time for the I2C host controller. If this is
> not done communication to slave devices may fail with arbitration lost
> errors like the one seen below taken from Lenovo Yoga 900:
> 
>   i2c_hid i2c-SYNA2B29:00: Fetching the HID descriptor
>   i2c_hid i2c-SYNA2B29:00: __i2c_hid_command: cmd=20 00
>   i2c_designware i2c_designware.1: i2c_dw_handle_tx_abort: lost arbitration
> 
> To fix this we follow what the Windows driver is doing and pass the default
> SDA hold time of 230 ns to all Intel Skylake host controllers. This still
> allows the platform to override these values by passing special ACPI
> methods SSCN and FMCN.
> 
> Reported-by: Kevin Fenzi <kevin@...ye.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

There has been a request to get this into stable:

https://bugzilla.kernel.org/show_bug.cgi?id=108581

Since we probably don't want to backport the whole device_property
series, is there a simpler fix to backport for stable?


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