linux-kernel - Re: [RFC 0/2] i2c-designware: Add support for AMD PSP semaphore

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Date:   Sat, 25 Dec 2021 17:58:51 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jan Dabros <jsd@...ihalf.com>, Hans de Goede <hdegoede@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Wolfram Sang <wsa@...nel.org>,
        Raul E Rangel <rrangel@...omium.org>,
        Marcin Wojtas <mw@...ihalf.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>, upstream@...ihalf.com
Subject: Re: [RFC 0/2] i2c-designware: Add support for AMD PSP semaphore

On Thu, Dec 23, 2021 at 4:43 PM Jan Dabros <jsd@...ihalf.com> wrote:
>
> This patchset comprises support for new i2c-designware controller setup on some
> AMD Cezanne SoCs, where x86 is sharing i2c bus with PSP. PSP uses the same
> controller and acts as an i2c arbitrator there (x86 is leasing bus from it).
>
> First commit aims to improve generic i2c-designware code by adding extra locking
> on probe() and disable() paths. I would like to ask someone with access to
> boards which use Intel BayTrail(CONFIG_I2C_DESIGNWARE_BAYTRAIL) to verify
> behavior of my changes on such setup.
>
> Second commit adds support for new PSP semaphore arbitration mechanism.
> Implementation is similar to the one from i2c-designware-baytrail.c however
> there are two main differences:
> 1) Add new ACPI ID in order to protect against silent binding of the old driver
> to the setup with PSP semaphore. Extra flag ARBITRATION_SEMAPHORE added to this
> new _HID allows to recognize setup with PSP.
> 2) Beside acquire_lock() and release_lock() methods we are also applying quirks
> to the lock_bus() and unlock_bus() global adapter methods. With this in place
> all i2c clients drivers may lock i2c bus for a desired number of i2c
> transactions (e.g. write-wait-read) without being aware of that such bus is
> shared with another entity.
>
> Mark this patchset as RFC, since waiting for new ACPI ID value. As a temporary
> measure use "AMDI9999". Once proper one will be ready, will re-send this CL for
> review & merge.
>
> Looking forward to some feedback.

When you will be ready, CC a new version also to Hans, he may look at
it from the Baytrail functionality perspective.

-- 
With Best Regards,
Andy Shevchenko