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

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Date:   Thu, 13 Feb 2020 14:19:14 -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,
        Enzo Matsumiya <ematsumiya@...e.com>
Subject: Re: [PATCH v3] PCI: pciehp: Make sure pciehp_isr clears interrupt
 events



On 2/10/20 3:40 PM, Stuart Hayes wrote:
> 
> 
> 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.
> 

CCing Enzo Matsumiya.