[PATCH] net: stmmac: dwxgmac2: enable L2 split header support

[Sagar Cheluvegowda <sagar.cheluvegowda@oss.qualcomm.com>]

XGMAC2 doesn't program the MAC extended configuration registers
needed for L2 header splitting when split-header mode is enabled,
so tagged AV packets can't use the split-header path. Configure
split mode (SPLM) and header saving (SAVE_EN) in XGMAC_EXT_CFG1,
extending the dwmac4 sequence added by commit d10f1a4e44c3 ("net:
stmmac: Programming sequence for VLAN packets with split header")
to XGMAC2.

Also fix the RX header-length calculation for split-header
descriptors. Per the XGMAC2 descriptor format, RDES3's L34T and
L2T fields are only valid on the last descriptor (LD set); on a
non-last descriptor they can hold stale write-back data from a
previous packet. Read the header length from RDES2[9:0] directly
for non-last descriptors, and only consult L34T/L2T on the last
descriptor: RDES2[9:0] for IP packets (L34T set) and RDES2[9:2]
for non-IP packets (L2T set).

Finally, disable the variable-length preamble when L2 splitting
is enabled. A variable-length preamble shifts the position of the
Ethernet header, making the L2 split offset non-deterministic.

Co-developed-by: Abhishek Chauhan <abhishek.chauhan@oss.qualcomm.com>
Signed-off-by: Abhishek Chauhan <abhishek.chauhan@oss.qualcomm.com>
Co-developed-by: Sarosh Hasan <sarosh.hasan@oss.qualcomm.com>
Signed-off-by: Sarosh Hasan <sarosh.hasan@oss.qualcomm.com>
Signed-off-by: Sagar Cheluvegowda <sagar.cheluvegowda@oss.qualcomm.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h       |  7 +++++++
 drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c | 12 +++++++++++-
 drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c   | 10 ++++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
index f8ab347f7b5b..3ccd29ea7ab0 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
@@ -167,6 +167,11 @@
 #define XGMAC_HW_FEATURE4		0x0000012c
 #define XGMAC_HWFEAT_EASP		BIT(4)
 #define XGMAC_HWFEAT_PCSEL		GENMASK(1, 0)
+#define XGMAC_EXT_CFG0			0x140
+#define XGMAC_EXT_CFG0_VPRE		BIT(8)
+#define XGMAC_EXT_CFG1			0x00000144
+#define XGMAC_CONFIG1_SAVE_EN		BIT(24)
+#define XGMAC_CONFIG1_SPLM(v)		FIELD_PREP(GENMASK(9, 8), v)
 #define XGMAC_MAC_DPP_FSM_INT_STATUS	0x00000150
 #define XGMAC_MAC_FSM_CONTROL		0x00000158
 #define XGMAC_PRTYEN			BIT(1)
@@ -434,6 +439,7 @@
 #define XGMAC_RDES2_L4FM		BIT(28)
 #define XGMAC_RDES2_L3FM		BIT(27)
 #define XGMAC_RDES2_HL			GENMASK(9, 0)
+#define XGMAC_RDES2_NONIPHL		GENMASK(9, 2)
 #define XGMAC_RDES3_OWN			BIT(31)
 #define XGMAC_RDES3_CTXT		BIT(30)
 #define XGMAC_RDES3_IOC			BIT(30)
@@ -441,6 +447,7 @@
 #define XGMAC_RDES3_CDA			BIT(27)
 #define XGMAC_RDES3_RSV			BIT(26)
 #define XGMAC_RDES3_L34T		GENMASK(23, 20)
+#define XGMAC_RDES3_L2T			GENMASK(19, 16)
 #define XGMAC_RDES3_ET_LT		GENMASK(19, 16)
 #define XGMAC_L34T_IP4TCP		0x1
 #define XGMAC_L34T_IP4UDP		0x2
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c
index 6719ac6e395b..65ac5403ec58 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c
@@ -292,8 +292,18 @@ static int dwxgmac2_get_rx_hash(struct dma_desc *p, u32 *hash,
 
 static void dwxgmac2_get_rx_header_len(struct dma_desc *p, unsigned int *len)
 {
-	if (le32_to_cpu(p->des3) & XGMAC_RDES3_L34T)
+	u32 rdes3 = le32_to_cpu(p->des3);
+
+	/* when FD=1 and LD=0, HL is RDES2[9:0] */
+	if (!(rdes3 & XGMAC_RDES3_LD)) {
+		*len = le32_to_cpu(p->des2) & XGMAC_RDES2_HL;
+		return;
+	}
+
+	if (rdes3 & XGMAC_RDES3_L34T)
 		*len = le32_to_cpu(p->des2) & XGMAC_RDES2_HL;
+	else if (rdes3 & XGMAC_RDES3_L2T)
+		*len = (le32_to_cpu(p->des2) & XGMAC_RDES2_NONIPHL) >> 2;
 }
 
 static void dwxgmac2_set_sec_addr(struct dma_desc *p, dma_addr_t addr, bool is_valid)
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
index ff83858ebc1f..0a9c787305a4 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
@@ -561,6 +561,16 @@ static void dwxgmac2_enable_sph(struct stmmac_priv *priv, void __iomem *ioaddr,
 	value |= XGMAC_CONFIG_HDSMS_256; /* Segment max 256 bytes */
 	writel(value, ioaddr + XGMAC_RX_CONFIG);
 
+	value = readl(ioaddr + XGMAC_EXT_CFG1);
+	value |= XGMAC_CONFIG1_SPLM(1);
+	value |= XGMAC_CONFIG1_SAVE_EN;
+	writel(value, ioaddr + XGMAC_EXT_CFG1);
+
+	/* Disable variable preambles to keep the L2 split offset deterministic. */
+	value = readl(ioaddr + XGMAC_EXT_CFG0);
+	value &= ~XGMAC_EXT_CFG0_VPRE;
+	writel(value, ioaddr + XGMAC_EXT_CFG0);
+
 	value = readl(ioaddr + XGMAC_DMA_CH_CONTROL(chan));
 	if (en)
 		value |= XGMAC_SPH;
-- 
2.34.1