PCI: Add arch_can_pci_mmap_wc() macro

Most of the almost-identical versions of pci_mmap_page_range() silently
ignore the 'write_combine' argument and give uncached mappings.

Yet we allow the PCIIOC_WRITE_COMBINE ioctl in /proc/bus/pci, expose the
'resourceX_wc' file in sysfs, and allow an attempted mapping to apparently
succeed.

To fix this, introduce a macro arch_can_pci_mmap_wc() which indicates
whether the platform can do a write-combining mapping.  On x86 this ends up
being pat_enabled(), while the few other platforms that support it can just
set it to a literal '1'.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
index 6ea1ced..25b7f1c 100644 (file)
--- a/Documentation/filesystems/sysfs-pci.txt
+++ b/Documentation/filesystems/sysfs-pci.txt
@@ -117,6 +117,10 @@ code must define HAVE_PCI_MMAP and provide a pci_mmap_page_range function.
 Platforms are free to only support subsets of the mmap functionality, but
 useful return codes should be provided.
 
+Platforms which support write-combining maps of PCI resources must define
+arch_can_pci_mmap_wc() which shall evaluate to non-zero at runtime when
+write-combining is permitted.
+
 Legacy resources are protected by the HAVE_PCI_LEGACY define.  Platforms
 wishing to support legacy functionality should define it and provide
 pci_legacy_read, pci_legacy_write and pci_mmap_legacy_page_range functions.

diff --git a/arch/ia64/include/asm/pci.h b/arch/ia64/include/asm/pci.h
index c0835b0..6283758 100644 (file)
--- a/arch/ia64/include/asm/pci.h
+++ b/arch/ia64/include/asm/pci.h
@@ -51,6 +51,8 @@ extern unsigned long ia64_max_iommu_merge_mask;
 #define PCI_DMA_BUS_IS_PHYS    (ia64_max_iommu_merge_mask == ~0UL)
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc() 1
+
 extern int pci_mmap_page_range (struct pci_dev *dev, struct vm_area_struct *vma,
                                enum pci_mmap_state mmap_state, int write_combine);
 #define HAVE_PCI_LEGACY

diff --git a/arch/powerpc/include/asm/pci.h b/arch/powerpc/include/asm/pci.h
index 93eded8..b5b68c6 100644 (file)
--- a/arch/powerpc/include/asm/pci.h
+++ b/arch/powerpc/include/asm/pci.h
@@ -81,8 +81,9 @@ struct vm_area_struct;
 int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
                        enum pci_mmap_state mmap_state, int write_combine);
 
-/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
-#define HAVE_PCI_MMAP  1
+/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() and it does WC */
+#define HAVE_PCI_MMAP          1
+#define arch_can_pci_mmap_wc() 1
 
 extern int pci_legacy_read(struct pci_bus *bus, loff_t port, u32 *val,
                           size_t count);

diff --git a/arch/x86/include/asm/pci.h b/arch/x86/include/asm/pci.h
index 1411dbe..f6e22c2 100644 (file)
--- a/arch/x86/include/asm/pci.h
+++ b/arch/x86/include/asm/pci.h
@@ -7,6 +7,7 @@
 #include <linux/string.h>
 #include <linux/scatterlist.h>
 #include <asm/io.h>
+#include <asm/pat.h>
 #include <asm/x86_init.h>
 
 #ifdef __KERNEL__
@@ -102,6 +103,7 @@ int pcibios_set_irq_routing(struct pci_dev *dev, int pin, int irq);
 
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc() pat_enabled()
 extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
                               enum pci_mmap_state mmap_state,
                               int write_combine);

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 7ac258f..7d494bd 100644 (file)
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -1211,9 +1211,9 @@ static int pci_create_resource_files(struct pci_dev *pdev)
 
                retval = pci_create_attr(pdev, i, 0);
                /* for prefetchable resources, create a WC mappable file */
-               if (!retval && pdev->resource[i].flags & IORESOURCE_PREFETCH)
+               if (!retval && arch_can_pci_mmap_wc() &&
+                   pdev->resource[i].flags & IORESOURCE_PREFETCH)
                        retval = pci_create_attr(pdev, i, 1);
-
                if (retval) {
                        pci_remove_resource_files(pdev);
                        return retval;

diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index dc8912e..a2aa58a 100644 (file)
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -210,14 +210,15 @@ static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
                break;
 
        case PCIIOC_WRITE_COMBINE:
-               if (arg)
-                       fpriv->write_combine = 1;
-               else
-                       fpriv->write_combine = 0;
-               break;
-
+               if (arch_can_pci_mmap_wc()) {
+                       if (arg)
+                               fpriv->write_combine = 1;
+                       else
+                               fpriv->write_combine = 0;
+                       break;
+               }
+               /* If arch decided it can't, fall through... */
 #endif /* HAVE_PCI_MMAP */
-
        default:
                ret = -EINVAL;
                break;

diff --git a/include/linux/pci.h b/include/linux/pci.h
index eb3da1a..e614fb4 100644 (file)
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1626,6 +1626,10 @@ static inline int pci_get_new_domain_nr(void) { return -ENOSYS; }
 
 #include <asm/pci.h>
 
+#ifndef arch_can_pci_mmap_wc
+#define arch_can_pci_mmap_wc()         0
+#endif
+
 #ifndef pci_root_bus_fwnode
 #define pci_root_bus_fwnode(bus)       NULL
 #endif