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From:   =?UTF-8?B?SmFuIETEhWJyb8Wb?= <jsd@semihalf.com>
Date:   Mon, 27 Dec 2021 08:00:09 +0100
Message-ID: <CAOtMz3NgF2Mq02PdGxKDkB33gtCq+vW7zNgW6nADUb+GMLBcxA@mail.gmail.com>
Subject: Re: [RFC 0/2] i2c-designware: Add support for AMD PSP semaphore
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Hans de Goede <hdegoede@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-i2c <linux-i2c@vger.kernel.org>,
        Jarkko Nikula <jarkko.nikula@linux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Wolfram Sang <wsa@kernel.org>,
        Raul E Rangel <rrangel@chromium.org>,
        Marcin Wojtas <mw@semihalf.com>,
        Grzegorz Jaszczyk <jaz@semihalf.com>, upstream@semihalf.com
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sob., 25 gru 2021 o 16:59 Andy Shevchenko <andy.shevchenko@gmail.com>
napisa=C5=82(a):
>
> On Thu, Dec 23, 2021 at 4:43 PM Jan Dabros <jsd@semihalf.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 s=
ame
> > 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 extr=
a 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 veri=
fy
> > 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 how=
ever
> > there are two main differences:
> > 1) Add new ACPI ID in order to protect against silent binding of the ol=
d 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 applyin=
g 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 bu=
s is
> > shared with another entity.
> >
> > Mark this patchset as RFC, since waiting for new ACPI ID value. As a te=
mporary
> > measure use "AMDI9999". Once proper one will be ready, will re-send thi=
s 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.

Thanks for the hint, it will be very helpful to have this tested on
Baytrail. From other comments on this RFC it seems that I would need
to affect Baytrail-semaphore path even more than initially thought.

Best Regards,
Jan