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Date:   Mon, 3 Oct 2022 23:14:12 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Lorenzo Pieralisi <lpieralisi@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>
Cc:     linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
Subject: Re: [EXT] Re: [PATCH v2] PCI: aardvark: Implement workaround for
 PCIe Completion Timeout
Message-ID: <20221003211412.5pqfjvcxyszd4ai6@pali>
References: <20220802123816.21817-1-pali@kernel.org>
 <20220926123434.2tqx4t6u3cnlrcx3@pali>
 <BN9PR18MB425117376E64340DED894178DB549@BN9PR18MB4251.namprd18.prod.outlook.com>
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Lorenzo, is something more needed for this patch? As it workarounds
crashing it is really needed to have it in mainline and backports.

On Wednesday 28 September 2022 14:05:10 Elad Nachman wrote:
> 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
> 
> External Email
> 
> ----------------------------------------------------------------------
> 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
> >