linux-kernel - Re: [PATCH v2 3/3] i2c: i801: Do not add ICH_RES_IO_SMI for the iTCO

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Message-ID: <20200310093136.GE1987@ninjato>
Date:   Tue, 10 Mar 2020 10:31:36 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Jean Delvare <jdelvare@...e.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Martin Volf <martin.volf.42@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        linux-i2c@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] i2c: i801: Do not add ICH_RES_IO_SMI for the
 iTCO_wdt device

On Wed, Feb 26, 2020 at 04:21:22PM +0300, Mika Westerberg wrote:
> Martin noticed that nct6775 driver does not load properly on his system
> in v5.4+ kernels. The issue was bisected to commit b84398d6d7f9 ("i2c:
> i801: Use iTCO version 6 in Cannon Lake PCH and beyond") but it is
> likely not the culprit because the faulty code has been in the driver
> already since commit 9424693035a5 ("i2c: i801: Create iTCO device on
> newer Intel PCHs"). So more likely some commit that added PCI IDs of
> recent chipsets made the driver to create the iTCO_wdt device on Martins
> system.
> 
> The issue was debugged to be PCI configuration access to the PMC device
> that is not present. This returns all 1's when read and this caused the
> iTCO_wdt driver to accidentally request resourses used by nct6775.
> 
> It turns out that the SMI resource is only required for some ancient
> systems, not the ones supported by this driver. For this reason do not
> populate the SMI resource at all and drop all the related code. The
> driver now always populates the main I/O resource and only in case of SPT
> (Intel Sunrisepoint) compatible devices it adds another resource for the
> NO_REBOOT bit. These two resources are of different types so
> platform_get_resource() used by the iTCO_wdt driver continues to find
> the both resources at index 0.
> 
> Link: https://lore.kernel.org/linux-hwmon/CAM1AHpQ4196tyD=HhBu-2donSsuogabkfP03v1YF26Q7_BgvgA@mail.gmail.com/
> Fixes: 9424693035a5 ("i2c: i801: Create iTCO device on newer Intel PCHs")
> Reported-by: Martin Volf <martin.volf.42@...il.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

I added a comment saying that the whole series is needed for a complete
fix. Dunno if there is a better way to express such dependencies for
stable.

Applied to for-current, thanks!


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