[PATCH net v4] net: stmmac: dwmac1000: clear the RGMII status interrupt

[Igor Velkov]

Since commit 2e2c878a3141 ("net: stmmac: remove SGMII/RGMII/SMII
interrupt handling") nothing on the RGMII path reads GMAC_RGSMIIIS, so
RGSMIIIS stays pending behind GMAC_INT_MASK from the first link change
on. stmmac_resume() resets the MAC in stmmac_hw_setup(); the reset sets
GMAC_INT_MASK to 0 until dwmac1000_core_init() writes the mask again,
and the pending status storms the line:

  dwmac_dma_interrupt: unexpected status 04000000

A register dump at the first message on ODROID-HC4 showed it:

  core int_status 00000001 int_mask 00000000 pmt 00000000 rgsmiiis 0000000d

When the resume thread runs on the CPU that takes the MAC interrupt,
the storm starves it: a soft lockup, then a watchdog reset or a hang.

Read GMAC_RGSMIIIS in dwmac1000_irq_status() when the status is not
masked, as the driver did before 2e2c878a3141; the read clears it.

Wake-on-LAN resume from s2idle with the resume thread and the MAC
interrupt on one CPU: Helios64 (dwmac-rk), 7.3-rc6, soft-locked in 3 of
3 resumes without a fix and in 0 of 10 with this patch; it ran with an
out-of-tree dwmac-rk change that keeps the GMAC powered across suspend.
ODROID-HC4 (dwmac-meson8b): 0 of 10 with this patch, 2 of 2 without a
fix on a 7.3-rc5 build. irq_rgmii_n went up by one per resume.

Fixes: 2e2c878a3141 ("net: stmmac: remove SGMII/RGMII/SMII interrupt handling")
Assisted-by: LLM
Signed-off-by: Igor Velkov <iav@xxxxxx>
---
v4:
- Clear RGSMIIIS in dwmac1000_irq_status() instead of disabling the
  interrupt line around stmmac_hw_setup() in stmmac_resume(), after
  Daniel Machon asked about a dwmac1000-only fix.
- Link to v3: https://lore.kernel.org/r/20261007031438.3179966-1-iav@xxxxxx

 drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c b/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
index d4ace3924891..66337cfd9824 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c
@@ -312,6 +312,12 @@ static int dwmac1000_irq_status(struct stmmac_priv *priv,
 	if (intr_status & (PCS_ANE_IRQ | PCS_LINK_IRQ))
 		stmmac_integrated_pcs_irq(priv, intr_status, x);
 
+	/* Reading RGSMIIIS clears the interrupt the MAC reset unmasks. */
+	if (intr_status & PCS_RGSMIIIS_IRQ) {
+		readl(ioaddr + GMAC_RGSMIIIS);
+		x->irq_rgmii_n++;
+	}
+
 	return ret;
 }
 
-- 
2.43.0