linux-kernel - Re: [PATCH 1/2] i2c: i2c-designware-platdrv: Allow a dynamic adap. nr without an ACPI fwnode

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Date:   Tue, 12 Mar 2019 17:05:13 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Lee Jones <lee.jones@...aro.org>, linux-i2c@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] i2c: i2c-designware-platdrv: Allow a dynamic adap.
 nr without an ACPI fwnode

On Tue, Mar 12, 2019 at 04:47:48PM +0200, Jarkko Nikula wrote:
> 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?

Seems like Hans came to the same conclusion.

> 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?

As far as I remember they are coming from ACPI, but you may easily check on
real hardware we have in our lab.

> 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?

-- 
With Best Regards,
Andy Shevchenko