linux-kernel - [PATCH 0/3] soundwire: use UniqueID only when relevant

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Message-Id: <20191022234808.17432-1-pierre-louis.bossart@linux.intel.com>
Date:   Tue, 22 Oct 2019 18:48:05 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     alsa-devel@...a-project.org
Cc:     linux-kernel@...r.kernel.org, tiwai@...e.de, broonie@...nel.org,
        vkoul@...nel.org, gregkh@...uxfoundation.org, jank@...ence.com,
        srinivas.kandagatla@...aro.org, slawomir.blauciak@...el.com,
        Bard liao <yung-chuan.liao@...ux.intel.com>,
        Rander Wang <rander.wang@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Subject: [PATCH 0/3] soundwire: use UniqueID only when relevant

The hardware UniqueID, typically enabled with pin-strapping, is
required during enumeration to avoid conflicts between devices of the
same type.

When there are no devices of the same type, using the UniqueID is
overkill and results in a lot of probe errors due to mismatches
between ACPI tables and hardware capabilities. For example it's not
uncommon for BIOS vendors to copy/paste the same settings between
platforms but the hardware pin-strapping is different. This is
perfectly legit and permitted by MIPI specs.

With this patchset, the UniqueID is only used when multiple devices of
the same type are detected. The loop to detect multiple identical
devices is not super efficient but with typically fewer than 4 devices
per link there's no real incentive to be smarter.

This change is only implemented for ACPI platforms, for DeviceTree
there is no change.

Pierre-Louis Bossart (3):
  soundwire: remove bitfield for unique_id, use u8
  soundwire: slave: add helper to extract slave ID
  soundwire: ignore uniqueID when irrelevant

 drivers/soundwire/bus.c       |  7 +--
 drivers/soundwire/slave.c     | 98 +++++++++++++++++++++++++++--------
 include/linux/soundwire/sdw.h |  4 +-
 3 files changed, 84 insertions(+), 25 deletions(-)

-- 
2.20.1