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Subject[PATCH v3 4/6] x86/PCI: allocate space from the end of a region, not the beginning
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Allocate from the end of a region, not the beginning.

For example, if we need to allocate 0x800 bytes for a device on bus
0000:00 given these resources:
[mem 0xbff00000-0xdfffffff] PCI Bus 0000:00
[mem 0xc0000000-0xdfffffff] PCI Bus 0000:02
the available space at [mem 0xbff00000-0xbfffffff] is passed to the
alignment callback (pcibios_align_resource()). Prior to this patch, we
would put the new 0x800 byte resource at the beginning of that available
space, i.e., at [mem 0xbff00000-0xbff007ff].
With this patch, we put it at the end, at [mem 0xbffff800-0xbfffffff].
Reference: https://bugzilla.kernel.org/show_bug.cgi?id=16228#c41
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
---
arch/x86/pci/i386.c | 18 ++++++++++++------
1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index 5525309..fe866c8 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -37,6 +37,7 @@
#include <asm/pci_x86.h>
#include <asm/io_apic.h>

+#define ALIGN_DOWN(x, a) ((x) & ~(a - 1))

static int
skip_isa_ioresource_align(struct pci_dev *dev) {
@@ -65,16 +66,21 @@ pcibios_align_resource(void *data, const struct resource *res,
resource_size_t size, resource_size_t align)
{
struct pci_dev *dev = data;
- resource_size_t start = res->start;
+ resource_size_t start = ALIGN_DOWN(res->end - size + 1, align);

if (res->flags & IORESOURCE_IO) {
- if (skip_isa_ioresource_align(dev))
- return start;
- if (start & 0x300)
- start = (start + 0x3ff) & ~0x3ff;
+
+ /*
+ * If we're avoiding ISA aliases, the largest contiguous I/O
+ * port space is 256 bytes. Clearing bits 9 and 10 preserves
+ * all 256-byte and smaller alignments, so the result will
+ * still be correctly aligned.
+ */
+ if (!skip_isa_ioresource_align(dev))
+ start &= ~0x300;
} else if (res->flags & IORESOURCE_MEM) {
if (start < BIOS_END)
- start = BIOS_END;
+ start = res->end; /* fail; no space */
}
return start;
}


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