linux-kernel - Re: [PATCH 1/1] PCI: armada8k: Disable LTSSM on link down interrupts

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Message-ID: <20241112214337.GA1861873@bhelgaas>
Date: Tue, 12 Nov 2024 15:43:37 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jenishkumar Maheshbhai Patel <jpatel2@...vell.com>
Cc: lpieralisi@...nel.org, thomas.petazzoni@...tlin.com, kw@...ux.com,
	manivannan.sadhasivam@...aro.org, robh@...nel.org,
	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	salee@...vell.com, dingwei@...vell.com
Subject: Re: [PATCH 1/1] PCI: armada8k: Disable LTSSM on link down interrupts

On Mon, Nov 11, 2024 at 10:42:41PM -0800, Jenishkumar Maheshbhai Patel wrote:
> When a PCI link down condition is detected, the link training state
> machine must be disabled immediately.

Why?

"Immediately" has no meaning here.  Arbitrary delays are possible and
must not break anything.

> Signed-off-by: Jenishkumar Maheshbhai Patel <jpatel2@...vell.com>
> ---
>  drivers/pci/controller/dwc/pcie-armada8k.c | 38 ++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-armada8k.c b/drivers/pci/controller/dwc/pcie-armada8k.c
> index b5c599ccaacf..07775539b321 100644
> --- a/drivers/pci/controller/dwc/pcie-armada8k.c
> +++ b/drivers/pci/controller/dwc/pcie-armada8k.c
> @@ -53,6 +53,10 @@ struct armada8k_pcie {
>  #define PCIE_INT_C_ASSERT_MASK		BIT(11)
>  #define PCIE_INT_D_ASSERT_MASK		BIT(12)
>  
> +#define PCIE_GLOBAL_INT_CAUSE2_REG	(PCIE_VENDOR_REGS_OFFSET + 0x24)
> +#define PCIE_GLOBAL_INT_MASK2_REG	(PCIE_VENDOR_REGS_OFFSET + 0x28)
> +#define PCIE_INT2_PHY_RST_LINK_DOWN	BIT(1)
> +
>  #define PCIE_ARCACHE_TRC_REG		(PCIE_VENDOR_REGS_OFFSET + 0x50)
>  #define PCIE_AWCACHE_TRC_REG		(PCIE_VENDOR_REGS_OFFSET + 0x54)
>  #define PCIE_ARUSER_REG			(PCIE_VENDOR_REGS_OFFSET + 0x5C)
> @@ -204,6 +208,11 @@ static int armada8k_pcie_host_init(struct dw_pcie_rp *pp)
>  	       PCIE_INT_C_ASSERT_MASK | PCIE_INT_D_ASSERT_MASK;
>  	dw_pcie_writel_dbi(pci, PCIE_GLOBAL_INT_MASK1_REG, reg);
>  
> +	/* Also enable link down interrupts */
> +	reg = dw_pcie_readl_dbi(pci, PCIE_GLOBAL_INT_MASK2_REG);
> +	reg |= PCIE_INT2_PHY_RST_LINK_DOWN;
> +	dw_pcie_writel_dbi(pci, PCIE_GLOBAL_INT_MASK2_REG, reg);
> +
>  	return 0;
>  }
>  
> @@ -221,6 +230,35 @@ static irqreturn_t armada8k_pcie_irq_handler(int irq, void *arg)
>  	val = dw_pcie_readl_dbi(pci, PCIE_GLOBAL_INT_CAUSE1_REG);
>  	dw_pcie_writel_dbi(pci, PCIE_GLOBAL_INT_CAUSE1_REG, val);
>  
> +	val = dw_pcie_readl_dbi(pci, PCIE_GLOBAL_INT_CAUSE2_REG);
> +
> +	if (PCIE_INT2_PHY_RST_LINK_DOWN & val) {
> +		u32 ctrl_reg = dw_pcie_readl_dbi(pci, PCIE_GLOBAL_CONTROL_REG);

Add blank line.

> +		/*
> +		 * The link went down. Disable LTSSM immediately. This
> +		 * unlocks the root complex config registers. Downstream
> +		 * device accesses will return all-Fs
> +		 */
> +		ctrl_reg &= ~(PCIE_APP_LTSSM_EN);
> +		dw_pcie_writel_dbi(pci, PCIE_GLOBAL_CONTROL_REG, ctrl_reg);

And here.

> +		/*
> +		 * Mask link down interrupts. They can be re-enabled once
> +		 * the link is retrained.
> +		 */
> +		ctrl_reg = dw_pcie_readl_dbi(pci, PCIE_GLOBAL_INT_MASK2_REG);
> +		ctrl_reg &= ~PCIE_INT2_PHY_RST_LINK_DOWN;
> +		dw_pcie_writel_dbi(pci, PCIE_GLOBAL_INT_MASK2_REG, ctrl_reg);

And here.  Follow existing coding style in this file.

> +		/*
> +		 * At this point a worker thread can be triggered to
> +		 * initiate a link retrain. If link retrains were
> +		 * possible, that is.
> +		 */
> +		dev_dbg(pci->dev, "%s: link went down\n", __func__);
> +	}
> +
> +	/* Now clear the second interrupt cause. */
> +	dw_pcie_writel_dbi(pci, PCIE_GLOBAL_INT_CAUSE2_REG, val);
> +
>  	return IRQ_HANDLED;
>  }
>  
> -- 
> 2.25.1
>