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

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Message-Id: <20211222094558.2098791-1-jsd@semihalf.com>
Date:   Wed, 22 Dec 2021 10:45:56 +0100
From:   Jan Dabros <jsd@...ihalf.com>
To:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        jarkko.nikula@...ux.intel.com
Cc:     andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
        wsa@...nel.org, rrangel@...omium.org, mw@...ihalf.com,
        jaz@...ihalf.com, jsd@...ihalf.com, upstream@...ihalf.com
Subject: [RFC 0/2] i2c-designware: Add support for AMD PSP semaphore

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.

Jan Dabros (2):
  i2c: designware: Add missing locks
  i2c: designware: Add AMD PSP I2C bus support

 MAINTAINERS                                 |   1 +
 drivers/acpi/acpi_apd.c                     |   1 +
 drivers/i2c/busses/Kconfig                  |  20 ++
 drivers/i2c/busses/Makefile                 |   1 +
 drivers/i2c/busses/i2c-designware-amdpsp.c  | 359 ++++++++++++++++++++
 drivers/i2c/busses/i2c-designware-common.c  |  12 +
 drivers/i2c/busses/i2c-designware-core.h    |   9 +-
 drivers/i2c/busses/i2c-designware-master.c  |   6 +
 drivers/i2c/busses/i2c-designware-platdrv.c |   3 +
 9 files changed, 411 insertions(+), 1 deletion(-)
 create mode 100644 drivers/i2c/busses/i2c-designware-amdpsp.c

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2.34.1.307.g9b7440fafd-goog