[PATCH net-next v2] net: stmmac: dwxgmac2: configure INTM for per-channel interrupt routing

[Zxyan Zhu <zxyan0222@gmail.com>]

The XGMAC DMA_MODE register has an INTM field (bits 13:12) that
controls interrupt routing behavior for DMA transfer completion
events:

  00 (default): sbd_perch_* are pulse signals, sbd_intr_o is also
                asserted for each completion event.
  01:          sbd_perch_* are level signals, sbd_intr_o is NOT
                asserted for packet transfer completion events.

When multi-MSI is enabled, per-channel TX/RX interrupts are expected
to arrive on their dedicated lines.  In the default INTM=00 mode,
sbd_intr_o also fires for DMA completion events, but the multi-MSI
handler stmmac_mac_interrupt() only processes MAC-layer events (LPI,
PMT, timestamps) and returns IRQ_NONE for every DMA completion
interrupt, resulting in a continuous stream of unhandled interrupts
on the common IRQ.

Hardware verification with XGMAC and multi-MSI enabled:

  INTM=00: 5.4 million common IRQ interrupts in 3 seconds, ~1.8
           million IRQ_NONE returns per second.
  INTM=01: 0 common IRQ interrupts, per-channel IRQs work normally,
           10G line rate works correctly.

Set INTM to mode 1 when multi-MSI is enabled.  This matches the
existing GMAC4 implementation.

XGMAC multi-MSI has never worked correctly since it was introduced.

Signed-off-by: Zxyan Zhu <zxyan0222@gmail.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h     |  2 ++
 drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
index 61b6d45a02f5..f8ab347f7b5b 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
@@ -320,6 +320,8 @@
 /* DMA Registers */
 #define XGMAC_DMA_MODE			0x00003000
 #define XGMAC_SWR			BIT(0)
+#define XGMAC_INTM_MASK			GENMASK(13, 12)
+#define XGMAC_INTM_MODE1		0x1
 #define XGMAC_DMA_SYSBUS_MODE		0x00003004
 #define XGMAC_WR_OSR_LMT		GENMASK(29, 24)
 #define XGMAC_RD_OSR_LMT		GENMASK(21, 16)
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
index 03437f1cf3df..ff83858ebc1f 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
@@ -31,6 +31,16 @@ static void dwxgmac2_dma_init(void __iomem *ioaddr,
 		value |= XGMAC_EAME;
 
 	writel(value, ioaddr + XGMAC_DMA_SYSBUS_MODE);
+
+	/*
+	 * Route DMA interrupts to per-channel lines when multi-MSI enabled.
+	 */
+	if (dma_cfg->multi_msi_en) {
+		value = readl(ioaddr + XGMAC_DMA_MODE);
+		value = u32_replace_bits(value, XGMAC_INTM_MODE1,
+					 XGMAC_INTM_MASK);
+		writel(value, ioaddr + XGMAC_DMA_MODE);
+	}
 }
 
 static void dwxgmac2_dma_init_chan(struct stmmac_priv *priv,

base-commit: 1df10cef2d1e7f9f2fb7eddb67fc70d3abf101f9
-- 
2.34.1