Re: [RESEND PATCH 5/5] PCI: aardvark: Implement workaround for PCIe Completion Timeout

["Pali Rohár" <pali@kernel.org>]

On Friday 25 June 2021 00:26:21 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.
> 
> 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>
> Cc: stable@vger.kernel.org
> ---
> Patch was originally written by Thomas and is already for a long time part
> of Marvell SDK. I have just re-written/re-applied it on top of mainline
> kernel and also wrote a new updated commit message.
> 
> Please note that this patch is questionable as Bjorn has some objections
> and nobody, including Marvell, was not able to explain erratum nor what
> is workaround exactly doing. Documentation about this topic is basically
> missing.

See also https://lore.kernel.org/linux-pci/20210723221710.wtztsrddudnxeoj3@pali/

> We just know that it fixes real kernel crashes when using WiFi cards.
> ---
>  drivers/pci/controller/pci-aardvark.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 9ff68abd8d1e..231f4469d87e 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -167,6 +167,8 @@
>  #define     LTSSM_L0				0x10
>  #define     RC_BAR_CONFIG			0x300
>  #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
> @@ -450,6 +452,11 @@ 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;
> -- 
> 2.20.1
>