[PATCH v3 13/14] net: axienet: Autodetect 64-bit DMA capability

[Andre Przywara <andre.przywara@arm.com>]

When newer revisions of the Axienet IP are configured for a 64-bit bus,
we *need* to write to the MSB part of the an address registers,
otherwise the IP won't recognise this as a DMA start condition.
This is even true when the actual DMA address comes from the lower 4 GB.

To autodetect this configuration, at probe time we write all 1's to such
an MSB register, and see if any bits stick. If this is configured for a
32-bit bus, those MSB registers are RES0, so reading back 0 indicates
that no MSB writes are necessary.
On the other hands reading anything other than 0 indicated the need to
write the MSB registers, so we set the respective flag.

The actual DMA mask stays at 32-bit for now. To help bisecting, a
separate patch will enable allocations from higher addresses.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/net/ethernet/xilinx/xilinx_axienet.h  |  1 +
 .../net/ethernet/xilinx/xilinx_axienet_main.c | 26 +++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet.h b/drivers/net/ethernet/xilinx/xilinx_axienet.h
index 84c4c3655516..fbaf3c987d9c 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet.h
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet.h
@@ -161,6 +161,7 @@
 #define XAE_FCC_OFFSET		0x0000040C /* Flow Control Configuration */
 #define XAE_EMMC_OFFSET		0x00000410 /* EMAC mode configuration */
 #define XAE_PHYC_OFFSET		0x00000414 /* RGMII/SGMII configuration */
+#define XAE_ID_OFFSET		0x000004F8 /* Identification register */
 #define XAE_MDIO_MC_OFFSET	0x00000500 /* MII Management Config */
 #define XAE_MDIO_MCR_OFFSET	0x00000504 /* MII Management Control */
 #define XAE_MDIO_MWD_OFFSET	0x00000508 /* MII Management Write Data */
diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 6ecd1bb5f81d..a54a5c754da0 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -151,6 +151,9 @@ static void axienet_dma_out_addr(struct axienet_local *lp, off_t reg,
 				 dma_addr_t addr)
 {
 	axienet_dma_out32(lp, reg, lower_32_bits(addr));
+
+	if (lp->features & XAE_FEATURE_DMA_64BIT)
+		axienet_dma_out32(lp, reg + 4, upper_32_bits(addr));
 }
 
 static void desc_set_phys_addr(struct axienet_local *lp, dma_addr_t addr,
@@ -1928,6 +1931,29 @@ static int axienet_probe(struct platform_device *pdev)
 		goto free_netdev;
 	}
 
+	/* Autodetect the need for 64-bit DMA pointers.
+	 * When the IP is configured for a bus width bigger than 32 bits,
+	 * writing the MSB registers is mandatory, even if they are all 0.
+	 * We can detect this case by writing all 1's to one such register
+	 * and see if that sticks: when the IP is configured for 32 bits
+	 * only, those registers are RES0.
+	 * Those MSB registers were introduced in IP v7.1, which we check first.
+	 */
+	if ((axienet_ior(lp, XAE_ID_OFFSET) >> 24) >= 0x9) {
+		void __iomem *desc = lp->dma_regs + XAXIDMA_TX_CDESC_OFFSET + 4;
+
+		iowrite32(0x0, desc);
+		if (ioread32(desc) == 0) {	/* sanity check */
+			iowrite32(0xffffffff, desc);
+			if (ioread32(desc) > 0) {
+				lp->features |= XAE_FEATURE_DMA_64BIT;
+				dev_info(&pdev->dev,
+					 "autodetected 64-bit DMA range\n");
+			}
+			iowrite32(0x0, desc);
+		}
+	}
+
 	/* Check for Ethernet core IRQ (optional) */
 	if (lp->eth_irq <= 0)
 		dev_info(&pdev->dev, "Ethernet core IRQ not defined\n");
-- 
2.17.1