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

[Pali Rohár]

Hello Elad, could you please review this patch? I have implemented it
according your instructions, including that full memory barrier as you
described.

On Tuesday 02 August 2022 14:38:16 Pali Rohár wrote:
> 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
>