[PATCH 4/5] PCI: mediatek-gen3: Don't reply AXI slave error

[Jianjun Wang <jianjun.wang@mediatek.com>]

There are some circumstances where the EP device will not respond to
non-posted access from the root port (e.g., MMIO read). In such cases,
the root port will reply with an AXI slave error, which will be treated
as a System Error (SError), causing a kernel panic and preventing us
from obtaining any useful information for further debugging.

We have added a new bit in the PCIE_AXI_IF_CTRL_REG register to prevent
PCIe AXI0 from replying with a slave error. Setting this bit on an older
platform that does not support this feature will have no effect.

By preventing AXI0 from replying with a slave error, we can keep the
kernel alive and debug using the information from AER.

Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
---
 drivers/pci/controller/pcie-mediatek-gen3.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
index 4bd3b39eebe2..48f83c2d91f7 100644
--- a/drivers/pci/controller/pcie-mediatek-gen3.c
+++ b/drivers/pci/controller/pcie-mediatek-gen3.c
@@ -87,6 +87,9 @@
 #define PCIE_LOW_POWER_CTRL_REG		0x194
 #define PCIE_FORCE_DIS_L0S		BIT(8)
 
+#define PCIE_AXI_IF_CTRL_REG		0x1a8
+#define PCIE_AXI0_SLV_RESP_MASK		BIT(12)
+
 #define PCIE_PIPE4_PIE8_REG		0x338
 #define PCIE_K_FINETUNE_MAX		GENMASK(5, 0)
 #define PCIE_K_FINETUNE_ERR		GENMASK(7, 6)
@@ -469,6 +472,15 @@ static int mtk_pcie_startup_port(struct mtk_gen3_pcie *pcie)
 	val |= PCIE_FORCE_DIS_L0S;
 	writel_relaxed(val, pcie->base + PCIE_LOW_POWER_CTRL_REG);
 
+	/*
+	 * Prevent PCIe AXI0 from replying a slave error, as it will cause kernel panic
+	 * and prevent us from getting useful information.
+	 * Keep the kernel alive and debug using the information from AER.
+	 */
+	val = readl_relaxed(pcie->base + PCIE_AXI_IF_CTRL_REG);
+	val |= PCIE_AXI0_SLV_RESP_MASK;
+	writel_relaxed(val, pcie->base + PCIE_AXI_IF_CTRL_REG);
+
 	/* Disable DVFSRC voltage request */
 	val = readl_relaxed(pcie->base + PCIE_MISC_CTRL_REG);
 	val |= PCIE_DISABLE_DVFSRC_VLT_REQ;
-- 
2.46.0