Re: [PATCH v2 1/8] PCI: pciehp: Rename pcie_isr() locals for clarity

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Sep 13, 2016 at 10:05:31AM +0000, Patel, Mayurkumar wrote:
>  
> > Rename "detected" and "intr_loc" to "status" and "events" for clarity.
> > "status" is the value we read from the Slot Status register; "events" is
> > the set of hot-plug events we need to process.  No functional change
> > intended.
> > 
> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > ---
> >  drivers/pci/hotplug/pciehp_hpc.c |   46 +++++++++++++++++++++-----------------
> >  1 file changed, 25 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> > index 08e84d6..264df36 100644
> > --- a/drivers/pci/hotplug/pciehp_hpc.c
> > +++ b/drivers/pci/hotplug/pciehp_hpc.c
> > @@ -542,7 +542,7 @@ static irqreturn_t pcie_isr(int irq, void *dev_id)
> >  	struct pci_bus *subordinate = pdev->subordinate;
> >  	struct pci_dev *dev;
> >  	struct slot *slot = ctrl->slot;
> > -	u16 detected, intr_loc;
> > +	u16 status, events;
> >  	u8 present;
> >  	bool link;
> > 
> > @@ -555,31 +555,35 @@ static irqreturn_t pcie_isr(int irq, void *dev_id)
> >  	 * serviced, we need to re-inspect Slot Status register after
> >  	 * clearing what is presumed to be the last pending interrupt.
> >  	 */
> > -	intr_loc = 0;
> > +	events = 0;
> >  	do {
> > -		pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &detected);
> > -		if (detected == (u16) ~0) {
> > +		pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &status);
> > +		if (status == (u16) ~0) {
> >  			ctrl_info(ctrl, "%s: no response from device\n",
> >  				  __func__);
> >  			return IRQ_HANDLED;
> >  		}
> > 
> > -		detected &= (PCI_EXP_SLTSTA_ABP | PCI_EXP_SLTSTA_PFD |
> > -			     PCI_EXP_SLTSTA_PDC |
> > -			     PCI_EXP_SLTSTA_CC | PCI_EXP_SLTSTA_DLLSC);
> > -		detected &= ~intr_loc;
> > -		intr_loc |= detected;
> > -		if (!intr_loc)
> > +		/*
> > +		 * Slot Status contains plain status bits as well as event
> > +		 * notification bits; right now we only want the event bits.
> > +		 */
> > +		status &= (PCI_EXP_SLTSTA_ABP | PCI_EXP_SLTSTA_PFD |
> > +			   PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_CC |
> > +			   PCI_EXP_SLTSTA_DLLSC);
> > +		status &= ~events;
> > +		events |= status;
> > +		if (!events)
> >  			return IRQ_NONE;
> > -		if (detected)
> > +		if (status)
> >  			pcie_capability_write_word(pdev, PCI_EXP_SLTSTA,
> > -						   intr_loc);
> > -	} while (detected);
> > +						   events);
> > +	} while (status);
> > 
> > -	ctrl_dbg(ctrl, "pending interrupts %#06x from Slot Status\n", intr_loc);
> > +	ctrl_dbg(ctrl, "pending interrupts %#06x from Slot Status\n", events);
> > 
> >  	/* Check Command Complete Interrupt Pending */
> > -	if (intr_loc & PCI_EXP_SLTSTA_CC) {
> > +	if (events & PCI_EXP_SLTSTA_CC) {
> >  		ctrl->cmd_busy = 0;
> >  		smp_mb();
> >  		wake_up(&ctrl->queue);
> > @@ -589,24 +593,24 @@ static irqreturn_t pcie_isr(int irq, void *dev_id)
> >  		list_for_each_entry(dev, &subordinate->devices, bus_list) {
> >  			if (dev->ignore_hotplug) {
> >  				ctrl_dbg(ctrl, "ignoring hotplug event %#06x (%s requested no hotplug)\n",
> > -					 intr_loc, pci_name(dev));
> > +					 events, pci_name(dev));
> >  				return IRQ_HANDLED;
> 
> Does it make sense here also to return IRQ_NONE? 

I don't think so.  Here's my reasoning; see if it makes sense:
IRQ_NONE means "I don't see any indication that my device needs
service."  If every handler for the IRQ returns IRQ_NONE, the
interrupt was spurious, and if we see enough spurious interrupts,
we'll disable that IRQ completely.  In this case, our device
definitely *did* request service; it's just that a driver wants us to
ignore hotplug events.  From the point of view of the kernel, we did
handle the IRQ (by ignoring it and clearing the interrupt request).

> >  			}
> >  		}
> >  	}
> > 
> > -	if (!(intr_loc & ~PCI_EXP_SLTSTA_CC))
> > +	if (!(events & ~PCI_EXP_SLTSTA_CC))
> >  		return IRQ_HANDLED;
> > 
> >  	/* Check Attention Button Pressed */
> > -	if (intr_loc & PCI_EXP_SLTSTA_ABP) {
> > +	if (events & PCI_EXP_SLTSTA_ABP) {
> >  		ctrl_info(ctrl, "Button pressed on Slot(%s)\n",
> >  			  slot_name(slot));
> >  		pciehp_queue_interrupt_event(slot, INT_BUTTON_PRESS);
> >  	}
> > 
> >  	/* Check Presence Detect Changed */
> > -	if (intr_loc & PCI_EXP_SLTSTA_PDC) {
> > +	if (events & PCI_EXP_SLTSTA_PDC) {
> >  		pciehp_get_adapter_status(slot, &present);
> >  		ctrl_info(ctrl, "Card %spresent on Slot(%s)\n",
> >  			  present ? "" : "not ", slot_name(slot));
> > @@ -615,13 +619,13 @@ static irqreturn_t pcie_isr(int irq, void *dev_id)
> >  	}
> > 
> >  	/* Check Power Fault Detected */
> > -	if ((intr_loc & PCI_EXP_SLTSTA_PFD) && !ctrl->power_fault_detected) {
> > +	if ((events & PCI_EXP_SLTSTA_PFD) && !ctrl->power_fault_detected) {
> >  		ctrl->power_fault_detected = 1;
> >  		ctrl_err(ctrl, "Power fault on slot %s\n", slot_name(slot));
> >  		pciehp_queue_interrupt_event(slot, INT_POWER_FAULT);
> >  	}
> > 
> > -	if (intr_loc & PCI_EXP_SLTSTA_DLLSC) {
> > +	if (events & PCI_EXP_SLTSTA_DLLSC) {
> >  		link = pciehp_check_link_active(ctrl);
> >  		ctrl_info(ctrl, "slot(%s): Link %s event\n",
> >  			  slot_name(slot), link ? "Up" : "Down");
> 
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