[PATCH net-next v3 07/13] net: lan966x: clear FDMA interrupt stickies after switch reset

[Daniel Machon <daniel.machon@microchip.com>]

When in PCI mode, the GCB soft reset issued by the reset controller
can latch spurious bits in the FDMA error stickies. The latched bits
sit in FDMA_INTR_ERR until the FDMA IRQ is requested later in probe,
at which point the handler fires immediately and WARNs.

Clear FDMA_ERRORS, FDMA_INTR_ERR and FDMA_INTR_DB right after the
switch reset so the FDMA comes out clean and the IRQ handler does not
see ghost errors on probe.

The clear runs on both the PCI and platform paths. On the platform
path it has no effect — there are no spurious stickies to clear — but
keeping it unconditional avoids a PCI-specific code path here.

Tested-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
---
 drivers/net/ethernet/microchip/lan966x/lan966x_main.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
index 9f69634ebb0a..b3701953b090 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
@@ -1064,6 +1064,15 @@ static int lan966x_reset_switch(struct lan966x *lan966x)
 
 	reset_control_reset(switch_reset);
 
+	/* When in PCI mode, the GCB soft reset issued by the reset
+	 * controller can latch spurious bits in the FDMA error stickies.
+	 * Clear them before request_irq hooks up the FDMA IRQ line,
+	 * otherwise the handler fires immediately on probe.
+	 */
+	lan_wr(lan_rd(lan966x, FDMA_ERRORS),   lan966x, FDMA_ERRORS);
+	lan_wr(lan_rd(lan966x, FDMA_INTR_ERR), lan966x, FDMA_INTR_ERR);
+	lan_wr(lan_rd(lan966x, FDMA_INTR_DB),  lan966x, FDMA_INTR_DB);
+
 	/* Don't reinitialize the switch core, if it is already initialized. In
 	 * case it is initialized twice, some pointers inside the queue system
 	 * in HW will get corrupted and then after a while the queue system gets

-- 
2.34.1