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36641b045c
xpcs_get_id() searches multiple MMDs for a known PHY ID, starting with MDIO_MMD_PCS (3). However not all integrators might have implemented that MMD on their MDIO bus. For example, the NXP SJA1105 and SJA1110 switches only implement vendor-specific MMD 1 and 2. When there is nothing on an MDIO bus at a certain address, traditionally the bus returns 0xffff, which means that the bus remained in its default pull-up state for the duration of the MDIO transaction. The 0xffff value is widely used in drivers/net/phy/phy_device.c (see get_phy_c22_id for example) to denote a missing device. So it makes sense for the xpcs to ignore this value as well, and continue its search, eventually finding the proper PHY ID in the vendor-specific MMDs. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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 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.