PCI: keystone: Add workaround for Errata #i2037 (AM65x SR 1.0)

Errata #i2037 in AM65x/DRA80xM Processors Silicon Revision 1.0
(SPRZ452D_July 2018_Revised December 2019 [1]) mentions when an
inbound PCIe TLP spans more than two internal AXI 128-byte bursts,
the bus may corrupt the packet payload and the corrupt data may
cause associated applications or the processor to hang.

The workaround for Errata #i2037 is to limit the maximum read
request size and maximum payload size to 128 bytes. Add workaround
for Errata #i2037 here.

The errata and workaround is applicable only to AM65x SR 1.0 and
later versions of the silicon will have this fixed.

[1] -> https://www.ti.com/lit/er/sprz452i/sprz452i.pdf

Link: https://lore.kernel.org/linux-pci/16e1fcae-1ea7-46be-b157-096e05661b15@siemens.comSigned-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Achal Verma <a-verma1@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Siddharth Vadapalli <s-vadapalli@ti.com>

drivers/pci/controller/dwc/pci-keystone.c

@@ -34,6 +34,11 @@
 #define PCIE_DEVICEID_SHIFT	16
 
 /* Application registers */
+#define PID				0x000
+#define RTL				GENMASK(15, 11)
+#define RTL_SHIFT			11
+#define AM6_PCI_PG1_RTL_VER		0x15
+
 #define CMD_STATUS			0x004
 #define LTSSM_EN_VAL		        BIT(0)
 #define OB_XLAT_EN_VAL		        BIT(1)
@@ -104,6 +109,8 @@
 
 #define to_keystone_pcie(x)		dev_get_drvdata((x)->dev)
 
+#define PCI_DEVICE_ID_TI_AM654X		0xb00c
+
 struct ks_pcie_of_data {
 	enum dw_pcie_device_mode mode;
 	const struct dw_pcie_host_ops *host_ops;
@@ -516,7 +523,11 @@ static int ks_pcie_start_link(struct dw_pcie *pci)
 static void ks_pcie_quirk(struct pci_dev *dev)
 {
 	struct pci_bus *bus = dev->bus;
+	struct keystone_pcie *ks_pcie;
+	struct device *bridge_dev;
 	struct pci_dev *bridge;
+	u32 val;
+
 	static const struct pci_device_id rc_pci_devids[] = {
 		{ PCI_DEVICE(PCI_VENDOR_ID_TI, PCIE_RC_K2HK),
 		 .class = PCI_CLASS_BRIDGE_PCI_NORMAL, .class_mask = ~0, },
@@ -528,6 +539,11 @@ static void ks_pcie_quirk(struct pci_dev *dev)
 		 .class = PCI_CLASS_BRIDGE_PCI_NORMAL, .class_mask = ~0, },
 		{ 0, },
 	};
+	static const struct pci_device_id am6_pci_devids[] = {
+		{ PCI_DEVICE(PCI_VENDOR_ID_TI, PCI_DEVICE_ID_TI_AM654X),
+		 .class = PCI_CLASS_BRIDGE_PCI << 8, .class_mask = ~0, },
+		{ 0, },
+	};
 
 	if (pci_is_root_bus(bus))
 		bridge = dev;
@@ -549,10 +565,36 @@ static void ks_pcie_quirk(struct pci_dev *dev)
 	 */
 	if (pci_match_id(rc_pci_devids, bridge)) {
 		if (pcie_get_readrq(dev) > 256) {
-			dev_info(&dev->dev, "limiting MRRS to 256\n");
+			dev_info(&dev->dev, "limiting MRRS to 256 bytes\n");
 			pcie_set_readrq(dev, 256);
 		}
 	}
+
+	/*
+	 * Memory transactions fail with PCI controller in AM654 PG1.0
+	 * when MRRS is set to more than 128 bytes. Force the MRRS to
+	 * 128 bytes in all downstream devices.
+	 */
+	if (pci_match_id(am6_pci_devids, bridge)) {
+		bridge_dev = pci_get_host_bridge_device(dev);
+		if (!bridge_dev && !bridge_dev->parent)
+			return;
+
+		ks_pcie = dev_get_drvdata(bridge_dev->parent);
+		if (!ks_pcie)
+			return;
+
+		val = ks_pcie_app_readl(ks_pcie, PID);
+		val &= RTL;
+		val >>= RTL_SHIFT;
+		if (val != AM6_PCI_PG1_RTL_VER)
+			return;
+
+		if (pcie_get_readrq(dev) > 128) {
+			dev_info(&dev->dev, "limiting MRRS to 128 bytes\n");
+			pcie_set_readrq(dev, 128);
+		}
+	}
 }
 DECLARE_PCI_FIXUP_ENABLE(PCI_ANY_ID, PCI_ANY_ID, ks_pcie_quirk);