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The KSZ9477 switch driver uses the XPCS driver to operate its SGMII port. However there are some hardware bugs in the KSZ9477 SGMII module so workarounds are needed. There was a proposal to update the XPCS driver to accommodate KSZ9477, but the new code is not generic enough to be used by other vendors. It is better to do all these workarounds inside the KSZ9477 driver instead of modifying the XPCS driver. There are 3 hardware issues. The first is the MII_ADVERTISE register needs to be write once after reset for the correct code word to be sent. The XPCS driver disables auto-negotiation first before configuring the SGMII/1000BASE-X mode and then enables it back. The KSZ9477 driver then writes the MII_ADVERTISE register before enabling auto-negotiation. In 1000BASE-X mode the MII_ADVERTISE register will be set, so KSZ9477 driver does not need to write it. The second issue is the MII_BMCR register needs to set the exact speed and duplex mode when running in SGMII mode. During link polling the KSZ9477 will check the speed and duplex mode are different from previous ones and update the MII_BMCR register accordingly. The last issue is 1000BASE-X mode does not work with auto-negotiation on. The cause is the local port hardware does not know the link is up and so network traffic is not forwarded. The workaround is to write 2 additional bits when 1000BASE-X mode is configured. Note the SGMII interrupt in the port cannot be masked. As that interrupt is not handled in the KSZ9477 driver the SGMII interrupt bit will not be set even when the XPCS driver sets it. Signed-off-by: Tristram Ha <tristram.ha@microchip.com> Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com> Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com> Link: https://patch.msgid.link/20250520230720.23425-1-Tristram.Ha@microchip.com Signed-off-by: Paolo Abeni <pabeni@redhat.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText 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.