Re: [PATCH] x86, pci: Add quirk for unsizeable Broadwell EP bar

[Andi Kleen <andi@firstfloor.org>]

On Fri, Feb 05, 2016 at 10:34:27AM -0600, Bjorn Helgaas wrote:
> On Fri, Feb 05, 2016 at 04:36:17AM +0100, Andi Kleen wrote:
> > > > But would actually anything use it?
> > > 
> > > You mean, would anything actually use the lspci output?  I don't know,
> > > but why would we want it to print garbage?
> > 
> > In he kernel. I don't think lspci is that interesting.
> > > 
> > > And the kernel certainly uses the struct resource.  Setting
> > > IORESOURCE_PCI_FIXED is not a way of saying "please ignore this
> > > resource."
> > 
> > There is already another quirk that uses the same technique to handle
> > a bad bar. I also didn't notice any bad side effects. Again what would it be
> > used for?
> 
> I suppose you mean pci_siemens_interrupt_controller(), added by
> 73a74ed3a6f8 ("PCI: i386: fixup for Siemens Nixdorf AG FSC
> Multiprocessor Interrupt Controllers")?
> 
> Here are the problems I see:

All good points. I changed the patch to use a new flag
IORESOURCE_PCI_IGNORE that skips the whole bar process
(except for the BAR size, which are ok in my case at least).

Also fixed to handle all BARs.

Does that look better?

------
x86, pci: Add quirk for unsizeable Broadwell EP bar
    
The Home Agent and PCU PCI devices in Broadwell-EP have a BAR that returns a
non zero value when read, but is still not sizeable (because it doesn't
exist).  This causes several [Firmware error] messages at boot. It does
not cause any functional problems, as the devices really have no BARs.

Add a PCI quirk to shut off the messages.

Since the message is printed before the normal header fixup add EARLY
fixups. This requires changing the PCI probe code to not override
the resource flags unconditionally, so that the quirk can set flags.

(I believe that's ok, they should be always zero before, but please double
check)

I used a new resource flag that causes the BAR to be ignored

v2: Handle all BARs, not just BAR0 (Chaohong Guo)
Switch over to using IORESOURCE_PCI_IGNORE over FIXED
Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
index e585655..837acb7 100644
--- a/arch/x86/pci/fixup.c
+++ b/arch/x86/pci/fixup.c
@@ -540,3 +540,18 @@ static void twinhead_reserve_killing_zone(struct pci_dev *dev)
         }
 }
 DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x27B9, twinhead_reserve_killing_zone);
+
+/*
+ * Intel Broadwell EP. Prevent reading/updating BARs on Home Agent and PCU devices
+ * which are not real BARs, but still return non-null.
+ * This prevents a harmless warning message at boot.
+ */
+static void pci_bdwep_ha_bar(struct pci_dev *dev)
+{
+	int i;
+
+	for (i = 0; i < 5; i++)
+		dev->resource[i].flags |= IORESOURCE_PCI_IGNORE;
+}
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x6fa0, pci_bdwep_ha_bar);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x6fc0, pci_bdwep_ha_bar);
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 6d7ab9b..7c12e6d 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -214,7 +214,9 @@ int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
 		l = 0;
 
 	if (type == pci_bar_unknown) {
-		res->flags = decode_bar(dev, l);
+		res->flags |= decode_bar(dev, l);
+		if (res->flags & IORESOURCE_PCI_IGNORE)
+			goto out;
 		res->flags |= IORESOURCE_SIZEALIGN;
 		if (res->flags & IORESOURCE_IO) {
 			l64 = l & PCI_BASE_ADDRESS_IO_MASK;
diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 24bea08..5262102 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -104,7 +104,7 @@ struct resource {
 
 /* PCI control bits.  Shares IORESOURCE_BITS with above PCI ROM.  */
 #define IORESOURCE_PCI_FIXED		(1<<4)	/* Do not move resource */
-
+#define IORESOURCE_PCI_IGNORE		(1<<5)	/* Ignore resource */
 
 /* helpers to define resources */
 #define DEFINE_RES_NAMED(_start, _size, _name, _flags)			\