linux-kernel - Re: [PATCH v3] PCI: pciehp: Make sure pciehp

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Date:   Mon, 10 Feb 2020 15:40:36 -0600
From:   Stuart Hayes <stuart.w.hayes@...il.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Austin Bolen <austin_bolen@...l.com>,
        Keith Busch <kbusch@...nel.org>,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, narendra_k@...l.com
Subject: Re: [PATCH v3] PCI: pciehp: Make sure pciehp_isr clears interrupt
 events



On 2/9/20 2:25 PM, Lukas Wunner wrote:
> On Sun, Feb 09, 2020 at 07:07:22PM +0100, Lukas Wunner wrote:
>> Actually, scratch that.  After thinking about this problem for a day
>> I've come up with a much simpler and more elegant solution.  Could you
>> test if the below works for you?
> 
> Sorry, I missed a few things:
> 
> * pm_runtime_put() is called too often in the MSI case.
> * If only the CC bit is set or if ignore_hotplug is set, the function
>   may return prematurely without re-reading the Slot Status register.
> * Returning IRQ_NONE in the MSI case even though the IRQ thread was woken
>   may incorrectly signal a spurious interrupt to the genirq code.
>   It's better to return IRQ_HANDLED instead.
> 
> Below is another attempt.  I'll have to take a look at this with a
> fresh pair of eyeballs though to verify I haven't overlooked anything
> else and also to determine if this is actually simpler than Stuart's
> approach.  Again, the advantage here is that processing of the events
> by the IRQ thread is sped up by not delaying it until the Slot Status
> register has settled.
> 
> Thanks.
> 
> -- >8 --
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index c3e3f53..db5baa5 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -530,6 +530,7 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
>  	struct controller *ctrl = (struct controller *)dev_id;
>  	struct pci_dev *pdev = ctrl_dev(ctrl);
>  	struct device *parent = pdev->dev.parent;
> +	irqreturn_t ret = IRQ_NONE;
>  	u16 status, events;
>  
>  	/*
> @@ -553,6 +554,7 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
>  		}
>  	}
>  
> +read_status:
>  	pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &status);
>  	if (status == (u16) ~0) {
>  		ctrl_info(ctrl, "%s: no response from device\n", __func__);
> @@ -579,13 +581,11 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
>  	if (!events) {
>  		if (parent)
>  			pm_runtime_put(parent);
> -		return IRQ_NONE;
> +		return ret;
>  	}
>  
>  	pcie_capability_write_word(pdev, PCI_EXP_SLTSTA, events);
>  	ctrl_dbg(ctrl, "pending interrupts %#06x from Slot Status\n", events);
> -	if (parent)
> -		pm_runtime_put(parent);
>  
>  	/*
>  	 * Command Completed notifications are not deferred to the
> @@ -595,21 +595,33 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
>  		ctrl->cmd_busy = 0;
>  		smp_mb();
>  		wake_up(&ctrl->queue);
> -
> -		if (events == PCI_EXP_SLTSTA_CC)
> -			return IRQ_HANDLED;
> -
>  		events &= ~PCI_EXP_SLTSTA_CC;
>  	}
>  
>  	if (pdev->ignore_hotplug) {
>  		ctrl_dbg(ctrl, "ignoring hotplug event %#06x\n", events);
> -		return IRQ_HANDLED;
> +		events = 0;
>  	}
>  
>  	/* Save pending events for consumption by IRQ thread. */
>  	atomic_or(events, &ctrl->pending_events);
> -	return IRQ_WAKE_THREAD;
> +
> +	/*
> +	 * In MSI mode, all event bits must be zero before the port will send
> +	 * a new interrupt (PCIe Base Spec r5.0 sec 6.7.3.4).  So re-read the
> +	 * Slot Status register in case a bit was set between read and write.
> +	 */
> +	if (pci_dev_msi_enabled(pdev) && !pciehp_poll_mode) {
> +		irq_wake_thread(irq, ctrl);
> +		ret = IRQ_HANDLED;
> +		goto read_status;
> +	}
> +
> +	if (parent)
> +		pm_runtime_put(parent);
> +	if (events)
> +		return IRQ_WAKE_THREAD;
> +	return IRQ_HANDLED;
>  }
>  
>  static irqreturn_t pciehp_ist(int irq, void *dev_id)
> 

I tested this patch, and it fixes the issue on my system.