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net: cadence: macb: implement EEE TX LPI support
The GEM MAC has hardware LPI registers (NCR bit 19: TXLPIEN) but no built-in idle timer, so asserting TXLPIEN blocks all TX immediately with no automatic wake. A software idle timer is required, as noted in Microchip documentation (section 40.6.19): "It is best to use firmware to control LPI." Implement phylink managed EEE using the mac_enable_tx_lpi and mac_disable_tx_lpi callbacks: - macb_tx_lpi_set(): sets or clears TXLPIEN; requires bp->lock to be held by the caller (asserted with lockdep_assert_held). Returns bool indicating whether the register actually changed, avoiding redundant writes and unnecessary udelay on the xmit fast path. - macb_tx_lpi_work_fn(): delayed_work handler that enters LPI if all TX queues are idle and EEE is still active. Takes bp->lock with irqsave before calling macb_tx_lpi_set(). - macb_tx_lpi_schedule(): arms the work timer using the LPI timer value provided by phylink (default 250 ms). Called from macb_tx_complete() after each TX drain so the idle countdown restarts whenever the ring goes quiet. - macb_tx_lpi_wake(): called from macb_start_xmit() under bp->lock, immediately before TSTART. Returns early if eee_active is false to avoid a register read on the common path when EEE is disabled. Clears TXLPIEN and applies a 50 us udelay for PHY wake (IEEE 802.3az Tw_sys_tx is 16.5 us for 1000BASE-T / 30 us for 100BASE-TX; GEM has no hardware enforcement). Only delays when TXLPIEN was actually set. The delay is placed after tx_head is advanced so the work_fn's queue-idle check sees a non-empty ring and cannot race back into LPI before the frame is transmitted. - mac_enable_tx_lpi: stores the timer and sets eee_active under bp->lock, then defers the first LPI entry by 1 second per IEEE 802.3az section 22.7a. - mac_disable_tx_lpi: cancels the work (sync, without the lock to avoid deadlock with the work_fn), then takes bp->lock to clear eee_active and deassert TXLPIEN. Populate phylink_config lpi_interfaces (MII, GMII, RGMII variants) and lpi_capabilities (MAC_100FD | MAC_1000FD) so phylink can negotiate EEE with the PHY and call the callbacks appropriately. Set lpi_timer_default to 250000 us and eee_enabled_default to true. Reviewed-by:Claudiu Beznea <claudiu.beznea@tuxon.dev> Reviewed-by:
Théo Lebrun <theo.lebrun@bootlin.com> Signed-off-by:
Nicolai Buchwitz <nb@tipi-net.de> Link: https://patch.msgid.link/20260304105432.631186-3-nb@tipi-net.de Signed-off-by:
Jakub Kicinski <kuba@kernel.org>