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Subject: Re: [PATCH 1/2] i2c: i2c-designware-platdrv: Allow a dynamic adap. nr
 without an ACPI fwnode
To:     Jarkko Nikula <jarkko.nikula@linux.intel.com>,
        Wolfram Sang <wsa@the-dreams.de>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Lee Jones <lee.jones@linaro.org>
Cc:     linux-i2c@vger.kernel.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20190311112216.31391-1-hdegoede@redhat.com>
 <20190311112216.31391-2-hdegoede@redhat.com>
 <c519b0ea-670d-defe-5870-c6258c19ff74@linux.intel.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <4b54ad0b-c3a7-3286-08bb-fda1cd243285@redhat.com>
Date:   Tue, 12 Mar 2019 15:51:51 +0100
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Hi,

On 12-03-19 15:47, Jarkko Nikula wrote:
> Hi
> 
> On 3/11/19 1:22 PM, Hans de Goede wrote:
>> Before this commit the i2c-designware-platdrv assumes that if the pdev
>> has an apci-companion it should use a dynamic adapter-nr and otherwise
>> it will use pdev->id as adapter-nr.
>>
>> On some devices e.g. the Apollo Lake using Acer TravelMate Spin B118,
>> some of the LPSS i2c-adapters are enumerated through PCI and do not have
>> an ACPI fwnode. These devices are handled as mfd devices so they end up
>> using the i2c-designware-platdrv driver.
>>
>> This results in the i2c-adapter being registered with the mfd generated
>> pdev->id as adapter-nr, which conflicts with existing adapters, triggering
>> a WARN(id < 0, "couldn't get idr") in i2c-core-base.c and causing the
>> adapter registration to fail.
>>
> I went thinking would we get a regression if we switch the i2c-designware-platdrv to dynamic numbering unconditionally?
> 
> Only drivers/mfd/intel-lpss.c and drivers/mfd/intel_quark_i2c_gpio.c register platform device "i2c_designware" and otherwise in the driver itself for known ACPI IDs and device tree bindings.
> 
> Things should be fine for ACPI cases if slave devices are also described in ACPI tables. As far as I've understood with device tree matching adapter number is irrelevant in slave device registration?
> 
> Andy: could you tell by commit 918fe70cf475 ("mfd: intel_quark_i2c_gpio: support devices behind i2c bus") are those devices described in ACPI or in some i2c_board_infos with referring to fixed adapter number either in or out of kernel tree code?
> 
> Then drivers/platform/chrome/chromeos_laptop.c is the only code searching for adapter named as "Synopsys DesignWare I2C adapter" without assuming any fixed adapter numbering.
> 
> What's unclear to me can there be device tree cases where i2c-designware probing comes with pdev->id not starting from zero or in different order? I.e. would it make difference do we use pdev->id or dynamic adapter numbering?

I've just completed analyzing all ways a designware_i2c (or compatible)
platform device can be instantiated and I've come to the conclusion that
always using dynamic adapter-nrs is fine and is a proper, clean fix for this.

Also see my reply to Andy which I send about the same time you send
your reply :)

Regards,

Hans