Re: [PATCH 1/2] PCI: Update BAR # and window messages

[Bjorn Helgaas <helgaas@kernel.org>]

On Sat, Nov 06, 2021 at 12:58:31PM +0100, Lukas Wunner wrote:
> On Sat, Nov 06, 2021 at 04:56:05PM +0530, Puranjay Mohan wrote:
> > +		switch (i) {
> > +		case 0: return "BAR 0";
> > +		case 1: return "BAR 1";
> > +		case 2: return "BAR 2";
> > +		case 3: return "BAR 3";
> > +		case 4: return "BAR 4";
> > +		case 5: return "BAR 5";
> > +		case PCI_ROM_RESOURCE: return "ROM";
> > +		#ifdef CONFIG_PCI_IOV
> > +		case PCI_IOV_RESOURCES + 0: return "VF BAR 0";
> > +		case PCI_IOV_RESOURCES + 1: return "VF BAR 1";
> > +		case PCI_IOV_RESOURCES + 2: return "VF BAR 2";
> > +		case PCI_IOV_RESOURCES + 3: return "VF BAR 3";
> > +		case PCI_IOV_RESOURCES + 4: return "VF BAR 4";
> > +		case PCI_IOV_RESOURCES + 5: return "VF BAR 5";
> > +		#endif
> > +		}
> 
> Use a static const array of char * instead of a switch/case ladder
> to reduce LoC count and improve performance.
> 
> See pcie_to_hpx3_type[] or state_conv[] in drivers/pci/pci-acpi.c
> for an example.

I tried converting this and came up with the below.  Is that the sort
of thing you're thinking?  Gcc *does* generate slightly smaller code
for it, but Puranjay's original source code is smaller and IMO a
little easier to read.

And I just noticed that Puranjay's code nicely returns "unknown" for
BAR 2-5 of bridges, while my code below does not.  Could be fixed, of
course, but would take a little more code.

  const char *pci_resource_name(struct pci_dev *dev, int i)
  {
	  static const char *bar_name[] = {
		  "BAR 0",
		  "BAR 1",
		  "BAR 2",
		  "BAR 3",
		  "BAR 4",
		  "BAR 5",
		  "ROM",
  #ifdef CONFIG_PCI_IOV
		  "VF BAR 0",
		  "VF BAR 1",
		  "VF BAR 2",
		  "VF BAR 3",
		  "VF BAR 4",
		  "VF BAR 5",
  #endif
		  "bridge I/O window",
		  "bridge mem window",
		  "bridge mem pref window",
	  };
	  static const char *cardbus_name[] = {
		  "BAR 0",
		  "unknown",
		  "unknown",
		  "unknown",
		  "unknown",
		  "unknown",
		  "unknown",
  #ifdef CONFIG_PCI_IOV
		  "unknown",
		  "unknown",
		  "unknown",
		  "unknown",
		  "unknown",
		  "unknown",
  #endif
		  "CardBus bridge I/O 0 window",
		  "CardBus bridge I/O 1 window",
		  "CardBus bridge mem 0 window",
		  "CardBus bridge mem 1 window",
	  };

	  if (dev->hdr_type == PCI_HEADER_TYPE_CARDBUS &&
	      i < ARRAY_SIZE(cardbus_name))
		  return cardbus_name[i];
	  else if (i < ARRAY_SIZE(bar_name))
		  return bar_name[i];

	  return "unknown";
  }