[PATCH v2] PCI: aardvark: Implement workaround for PCIe Completion Timeout

[Pali Rohár]

Marvell Armada 3700 Functional Errata, Guidelines, and Restrictions
document describes in erratum 3.12 PCIe Completion Timeout (Ref #: 251),
that PCIe IP does not support a strong-ordered model for inbound posted vs.
outbound completion.

As a workaround for this erratum, DIS_ORD_CHK flag in Debug Mux Control
register must be set. It disables the ordering check in the core between
Completions and Posted requests received from the link.

Marvell also suggests to do full memory barrier at the beginning of
aardvark summary interrupt handler before calling interrupt handlers of
endpoint drivers in order to minimize the risk for the race condition
documented in the Erratum between the DMA done status reading and the
completion of writing to the host memory.

More details about this issue and suggested workarounds are in discussion:
https://lore.kernel.org/linux-pci/BN9PR18MB425154FE5019DCAF2028A1D5DB8D9@BN9PR18MB4251.namprd18.prod.outlook.com/t/#u

It was reported that enabling this workaround fixes instability issues and
"Unhandled fault" errors when using 60 GHz WiFi 802.11ad card with Qualcomm
QCA6335 chip under significant load which were caused by interrupt status
stuck in the outbound CMPLT queue traced back to this erratum.

This workaround fixes also kernel panic triggered after some minutes of
usage 5 GHz WiFi 802.11ax card with Mediatek MT7915 chip:

    Internal error: synchronous external abort: 96000210 [#1] SMP
    Kernel panic - not syncing: Fatal exception in interrupt

Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
Signed-off-by: Pali Rohár <pali at kernel.org>
Fixes: 8c39d710363c ("PCI: aardvark: Add Aardvark PCI host controller driver")
Cc: stable at vger.kernel.org
---
 drivers/pci/controller/pci-aardvark.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index 060936ef01fe..3ae8a85ec72e 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c
@@ -210,6 +210,8 @@ enum {
 };
 
 #define VENDOR_ID_REG				(LMI_BASE_ADDR + 0x44)
+#define DEBUG_MUX_CTRL_REG			(LMI_BASE_ADDR + 0x208)
+#define     DIS_ORD_CHK				BIT(30)
 
 /* PCIe core controller registers */
 #define CTRL_CORE_BASE_ADDR			0x18000
@@ -558,6 +560,11 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
 		PCIE_CORE_CTRL2_TD_ENABLE;
 	advk_writel(pcie, reg, PCIE_CORE_CTRL2_REG);
 
+	/* Disable ordering checks, workaround for erratum 3.12 "PCIe completion timeout" */
+	reg = advk_readl(pcie, DEBUG_MUX_CTRL_REG);
+	reg |= DIS_ORD_CHK;
+	advk_writel(pcie, reg, DEBUG_MUX_CTRL_REG);
+
 	/* Set lane X1 */
 	reg = advk_readl(pcie, PCIE_CORE_CTRL0_REG);
 	reg &= ~LANE_CNT_MSK;
@@ -1581,6 +1588,9 @@ static irqreturn_t advk_pcie_irq_handler(int irq, void *arg)
 	struct advk_pcie *pcie = arg;
 	u32 status;
 
+	/* Full memory barrier (ARM dsb sy), workaround for erratum 3.12 "PCIe completion timeout" */
+	mb();
+
 	status = advk_readl(pcie, HOST_CTRL_INT_STATUS_REG);
 	if (!(status & PCIE_IRQ_CORE_INT))
 		return IRQ_NONE;
-- 
2.20.1