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

[Elad Nachman <enachman@marvell.com>]

Reviewed-by: Elad Nachman <enachman@marvell.com>

Thanks,

Elad.

-----Original Message-----
From: Pali Rohár <pali@kernel.org> 
Sent: Monday, September 26, 2022 3:35 PM
To: Elad Nachman <enachman@marvell.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>; Lorenzo Pieralisi <lpieralisi@kernel.org>; Bjorn Helgaas <bhelgaas@google.com>; Krzysztof Wilczyński <kw@linux.com>; Rob Herring <robh@kernel.org>; linux-pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; Gregory Clement <gregory.clement@bootlin.com>; Marek Behún <kabel@kernel.org>; Remi Pommarel <repk@triplefau.lt>; Xogium <contact@xogium.me>; Tomasz Maciej Nowak <tmn505@gmail.com>
Subject: [EXT] Re: [PATCH v2] PCI: aardvark: Implement workaround for PCIe Completion Timeout

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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://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_l
> inux-2Dpci_BN9PR18MB425154FE5019DCAF2028A1D5DB8D9-40BN9PR18MB4251.namp
> rd18.prod.outlook.com_t_-23u&d=DwIDaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=eTeNT
> LEK5-TxXczjOcKPhANIFtlB9pP4lq9qhdlFrwQ&m=bjgkhgPgOjqCEsbHYHONCZMiFDX72
> MztWaE0AvWBktQVn3zKEDtUdn02Kx_KJ14B&s=SToGsDGEObwbZGilVtVZPyME8jNiRgrq
> 4SDYvqqT0TA&e=
> 
> 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@bootlin.com>
> Signed-off-by: Pali Rohár <pali@kernel.org>
> Fixes: 8c39d710363c ("PCI: aardvark: Add Aardvark PCI host controller 
> driver")
> Cc: stable@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
>