linux-kernel - Re: [PATCH 2/3] PCI: dwc: pci-dra7xx: Improve MSI IRQ handling

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Message-ID: <20180212175801.GA29070@e107981-ln.cambridge.arm.com>
Date:   Mon, 12 Feb 2018 17:58:01 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Vignesh R <vigneshr@...com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Niklas Cassel <niklas.cassel@...s.com>,
        linux-omap@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] PCI: dwc: pci-dra7xx: Improve MSI IRQ handling

On Fri, Feb 09, 2018 at 05:34:14PM +0530, Vignesh R wrote:
> We need to ensure that there are no pending MSI IRQ vector set (i.e
> PCIE_MSI_INTR0_STATUS reads 0 at least once) before exiting
> dra7xx_pcie_msi_irq_handler(). Else, the dra7xx PCIe wrapper will not
> register new MSI IRQs even though PCIE_MSI_INTR0_STATUS shows IRQs are
> pending. Therefore, keep calling dra7xx_pcie_msi_irq_handler() until it
> returns IRQ_NONE, which suggests that PCIE_MSI_INTR0_STATUS is 0.
> 
> This fixes a bug, where PCIe wifi cards with 4 DMA queues like Intel
> 8260 used to throw following error and stall during ping/iperf3 tests.
> 
> [   97.776310] iwlwifi 0000:01:00.0: Queue 9 stuck for 2500 ms.
> 
> Signed-off-by: Vignesh R <vigneshr@...com>
> ---
>  drivers/pci/dwc/pci-dra7xx.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/dwc/pci-dra7xx.c b/drivers/pci/dwc/pci-dra7xx.c
> index ed8558d638e5..3420cbf7b60a 100644
> --- a/drivers/pci/dwc/pci-dra7xx.c
> +++ b/drivers/pci/dwc/pci-dra7xx.c
> @@ -254,14 +254,31 @@ static irqreturn_t dra7xx_pcie_msi_irq_handler(int irq, void *arg)
>  	struct dra7xx_pcie *dra7xx = arg;
>  	struct dw_pcie *pci = dra7xx->pci;
>  	struct pcie_port *pp = &pci->pp;
> +	int count = 0;
>  	unsigned long reg;
>  	u32 virq, bit;
>  
>  	reg = dra7xx_pcie_readl(dra7xx, PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI);
> +	dra7xx_pcie_writel(dra7xx, PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI, reg);
>  
>  	switch (reg) {
>  	case MSI:
> -		dw_handle_msi_irq(pp);
> +		/*
> +		 * Need to make sure no MSI IRQs are pending before
> +		 * exiting handler, else the wrapper will not catch new
> +		 * IRQs. So loop around till dw_handle_msi_irq() returns
> +		 * IRQ_NONE
> +		 */
> +		while (dw_handle_msi_irq(pp) != IRQ_NONE && count < 1000)
> +			count++;
> +
> +		if (count == 1000) {
> +			dev_err(pci->dev, "too much work in msi irq\n");
> +			dra7xx_pcie_writel(dra7xx,
> +					   PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI,
> +					   reg);
> +			return IRQ_HANDLED;

I am not merging any code patching this IRQ handling routine anymore
unless you thoroughly explain to me how this CONF_IRQSTATUS_MSI register
works (and how it is related to DW registers) and why this specific host
controller needs handling that is not required by any other host
controller relying on dw_handle_msi_irq().

I suspect there is a code design flaw with the way this host handles
IRQs and we are going to find it and fix it the way it should, not with
any plaster like this patch.

Lorenzo

> +		}
>  		break;
>  	case INTA:
>  	case INTB:
> @@ -275,8 +292,6 @@ static irqreturn_t dra7xx_pcie_msi_irq_handler(int irq, void *arg)
>  		break;
>  	}
>  
> -	dra7xx_pcie_writel(dra7xx, PCIECTRL_DRA7XX_CONF_IRQSTATUS_MSI, reg);
> -
>  	return IRQ_HANDLED;
>  }
>  
> -- 
> 2.16.1
>