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

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Date:   Wed, 22 Dec 2021 13:46:07 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jan Dabros <jsd@...ihalf.com>,
        Serge Semin <fancer.lancer@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        jarkko.nikula@...ux.intel.com, mika.westerberg@...ux.intel.com,
        wsa@...nel.org, rrangel@...omium.org, mw@...ihalf.com,
        jaz@...ihalf.com, upstream@...ihalf.com
Subject: Re: [RFC 0/2] i2c-designware: Add support for AMD PSP semaphore

+Serge

On Wed, Dec 22, 2021 at 10:45:56AM +0100, Jan Dabros 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.

If I am not mistaken something similar happened in Baikal T1.
Perhaps Serge has something to share.

-- 
With Best Regards,
Andy Shevchenko