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014f0c98cf
Implement the KSZ87xx short cable workaround. This patch implements the KSZ87xx short cable erratum described in Microchip document DS80000687C for KSZ87xx switches and the following support article: Link: https://support.microchip.com/s/article/Solution-for-Using-CAT-5E-or-CAT-6-Short-Cable-with-a-Link-Issue-for-the-KSZ8795-Family The issue affects short or low-loss cable links (e.g. CAT5e/CAT6), where the PHY receiver equalizer may amplify high-amplitude signals excessively, resulting in internal distortion and link establishment failures. KSZ87xx devices require a workaround for the Module 3 low-loss cable condition, controlled through the switch TABLE_LINK_MD_V indirect registers. This change models the erratum handling as vendor-specific Clause 22 PHY registers, virtualized by the KSZ8 DSA driver and accessed via ksz8_r_phy() / ksz8_w_phy(). The following controls are provided: - A boolean “short-cable” preset, which applies a documented and conservative configuration (LPF 62 MHz bandwidth and DSP EQ initial value 0), and is the recommended interface for typical use cases. - Separate LPF bandwidth and DSP EQ initial value controls intended for advanced or experimental tuning. These are orthogonal and independent, and override the corresponding settings without requiring any specific ordering. The preset and tunables act as simple setters with no implicit state machine or invalid combinations, keeping the API predictable and aligned with the KISS principle. The erratum affects the shared PHY analog front-end and therefore applies globally to the switch. Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de> Reviewed-by: Marek Vasut <marex@nabladev.com> Signed-off-by: Fidelio Lawson <fidelio.lawson@exotec.com> Link: https://patch.msgid.link/20260609-ksz87xx_errata_low_loss_connections-v10-1-9ba4418cf3db@exotec.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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