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Bard Liao 5bb643c39b soundwire: add master quirks for bus clash and parity
Currently quirks are only allowed for Slave devices. This patch
describes the need for two quirks at the Master level.

a) bus clash
The SoundWire specification allows a Slave device to report a bus clash
with the in-band interrupt mechanism when it detects a conflict while
driving a bitSlot it owns. This can be a symptom of an electrical conflict
or a programming error, and it's vital to detect reliably.

Unfortunately, on some platforms, bus clashes are randomly reported by
Slave devices after a bus reset, with an interrupt status set even before
the bus clash interrupt is enabled. These initial spurious interrupts are
not relevant and should optionally be filtered out, while leaving the
interrupt mechanism enabled to detect 'true' issues.

This patch suggests the addition of a Master level quirk to discard such
interrupts. The quirk should in theory have been added at the Slave level,
but since the problem was detected with different generations of Slave
devices it's hard to point to a specific IP. The problem might also be
board-dependent and hence dealing with a Master quirk is simpler.

b) parity

Additional tests on a new platform with the Maxim 98373 amplifier
showed a rare case where the parity interrupt is also thrown on
startup, at the same time as bus clashes. This issue only seems to
happen infrequently and was only observed during suspend-resume stress
tests while audio is streaming. We could make the problem go away by
adding a Slave-level quirk, but there is no evidence that the issue is
actually a Slave problem: the parity is provided by the Master, which
could also set an invalid parity in corner cases.

BugLink: https://github.com/thesofproject/linux/issues/2578
BugLink: https://github.com/thesofproject/linux/issues/2533
Co-developed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Link: https://lore.kernel.org/r/20210302082720.12322-2-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
2021-03-22 17:46:39 +05:30
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Makefile Linux 5.12-rc2 2021-03-05 17:33:41 -08:00
README

Linux kernel
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In order to build the documentation, use ``make htmldocs`` or
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    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.