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

["Pali Rohár" <pali@kernel.org>]

On Wednesday 25 August 2021 21:59:53 Pali Rohár wrote:
> 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/

Hello Lorenzo. For now let just this one patch (5/5) as is. As we do not
know how to process this issue and there is open (above) question.

I hope that Marvell people would respond to this above issue.

Other remaining patches in this series are fine.

> > 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
> >