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Use software polling (PHY_POLL) to check for link state changes instead of relying on the EMAC's hardware polling feature. Some PHY drivers are unable to get a functioning link because the HW polling is not robust enough. The EMAC is able to poll the PHY on the MDIO bus looking for link state changes (via the Link Status bit in the Status Register at address 0x1). When the link state changes, the EMAC triggers an interrupt and tells the driver what the new state is. The feature eliminates the need for software to poll the MDIO bus. Unfortunately, this feature is incompatible with phylib, because it ignores everything that the PHY core and PHY drivers are trying to do. In particular: 1. It assumes a compatible register set, so PHYs with different registers may not work. 2. It doesn't allow for hardware errata that have work-arounds implemented in the PHY driver. 3. It doesn't support multiple register pages. If the PHY core switches the register set to another page, the EMAC won't know the page has changed and will still attempt to read the same PHY register. 4. It only checks the copper side of the link, not the SGMII side. Some PHY drivers (e.g. at803x) may also check the SGMII side, and report the link as not ready during autonegotiation if the SGMII link is still down. Phylib then waits for another interrupt to query the PHY again, but the EMAC won't send another interrupt because it thinks the link is up. Cc: stable@vger.kernel.org # 4.11.x Tested-by: Manoj Iyer <manoj.iyer@canonical.com> Signed-off-by: Timur Tabi <timur@codeaurora.org> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.