[PATCH 1/1] PCI: ignore failure to preallocate minimal resources to hotplug bridges

[Ram Pai <linuxram@us.ibm.com>]

        PCI: ignore failure to preallocate minimal resources to 
		hotplug bridges

	Linux tries to pre-allocate minimal resources to hotplug 
	bridges.  This 	works 	fine as long as there are enough 
	resources  to  satisfy   all   other   genuine  resource
	requirements.  However  if  enough  resources   are  not 
	available    to    satisfy    the    pre-allocation, the 
	resource-allocator reports errors and returns failure.
	
	This patch distinguishes between must-need resources and
	nice-to-have   resources.   Any   failure   to  allocate 
	nice-to-have resources are ignored. 

	This  behavior  can  be  particularly  useful to trigger 
	automatic  reallocation, if  the  OS  discovers  genuine 
	resource  allocation  conflicts  or  genuine unallocated 
	BARs  caused  by not-so-smart allocation behavior of the 
	native BIOS.

	The motivation for this patch is due a issue reported in 
	https://bugzilla.kernel.org/show_bug.cgi?id=15960

Signed-off-by: Ram Pai <linuxram@us.ibm.com>

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 66cb8f4..3bbc427 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -412,14 +412,14 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size)
 {
 	struct pci_dev *dev;
 	struct resource *b_res = find_free_bus_resource(bus, IORESOURCE_IO);
-	unsigned long size = 0, size1 = 0, old_size;
+	unsigned long size = 0, size1 = 0, old_size, dev_present=0;
 
 	if (!b_res)
  		return;
 
 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		int i;
-
+		dev_present=1;
 		for (i = 0; i < PCI_NUM_RESOURCES; i++) {
 			struct resource *r = &dev->resource[i];
 			unsigned long r_size;
@@ -460,6 +460,12 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size)
 	b_res->start = 4096;
 	b_res->end = b_res->start + size - 1;
 	b_res->flags |= IORESOURCE_STARTALIGN;
+
+	/* if no devices are behind this bus, inform
+	 * resource-allocater to try hard but not to worry
+	 * if allocations fail 
+	 */
+	b_res->flags |= (!dev_present) ? IORESOURCE_IGNORE_FAIL : 0;
 }
 
 /* Calculate the size of the bus and minimal alignment which
@@ -470,7 +476,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	struct pci_dev *dev;
 	resource_size_t min_align, align, size, old_size;
 	resource_size_t aligns[12];	/* Alignments from 1Mb to 2Gb */
-	int order, max_order;
+	int order, max_order, dev_present=0;
 	struct resource *b_res = find_free_bus_resource(bus, type);
 	unsigned int mem64_mask = 0;
 
@@ -487,6 +493,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		int i;
 
+		dev_present=1;
 		for (i = 0; i < PCI_NUM_RESOURCES; i++) {
 			struct resource *r = &dev->resource[i];
 			resource_size_t r_size;
@@ -550,6 +557,13 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	b_res->end = size + min_align - 1;
 	b_res->flags |= IORESOURCE_STARTALIGN;
 	b_res->flags |= mem64_mask;
+
+	/* if no devices are behind this bus, inform
+	 * resource-allocater to try hard but not to worry
+	 * if allocations fail 
+	 */
+	b_res->flags |= (!dev_present) ? IORESOURCE_IGNORE_FAIL : 0;
+
 	return 1;
 }
 
diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index 2aaa131..a8ce953 100644
--- a/drivers/pci/setup-res.c
+++ b/drivers/pci/setup-res.c
@@ -210,7 +210,8 @@ int pci_assign_resource(struct pci_dev *dev, int resno)
 	if (!align) {
 		dev_info(&dev->dev, "BAR %d: can't assign %pR "
 			 "(bogus alignment)\n", resno, res);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	bus = dev->bus;
@@ -225,6 +226,10 @@ int pci_assign_resource(struct pci_dev *dev, int resno)
 	}
 
 	if (ret) {
+		if (res->flags & IORESOURCE_IGNORE_FAIL) {
+			ret = 0;
+			goto out;
+		}
 		if (res->flags & IORESOURCE_MEM)
 			if (res->flags & IORESOURCE_PREFETCH)
 				type = "mem pref";
@@ -239,6 +244,8 @@ int pci_assign_resource(struct pci_dev *dev, int resno)
 			 resno, type, (unsigned long long) resource_size(res));
 	}
 
+out:
+	res->flags &= ~IORESOURCE_IGNORE_FAIL;
 	return ret;
 }
 
diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index b227902..941624b 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -49,6 +49,7 @@ struct resource_list {
 
 #define IORESOURCE_SIZEALIGN	0x00040000	/* size indicates alignment */
 #define IORESOURCE_STARTALIGN	0x00080000	/* start field is alignment */
+#define IORESOURCE_IGNORE_FAIL	0x00800000 	/* IGNORE if allocation fail*/
 
 #define IORESOURCE_MEM_64	0x00100000
 #define IORESOURCE_WINDOW	0x00200000	/* forwarded by bridge */