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Subject[PATCH v2 05/27] pci: Add arch_can_pci_mmap_wc() macro
Date
From: David Woodhouse <dwmw@amazon.co.uk>

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>
---
Documentation/filesystems/sysfs-pci.txt | 4 ++++
arch/ia64/include/asm/pci.h | 2 ++
arch/powerpc/include/asm/pci.h | 5 +++--
arch/x86/include/asm/pci.h | 2 ++
drivers/pci/pci-sysfs.c | 4 ++--
drivers/pci/proc.c | 15 ++++++++-------
include/linux/pci.h | 4 ++++
7 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
index 6ea1ced..25b7f1c 100644
--- 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
--- 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
--- 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
--- 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
--- 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
--- 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
--- 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
--
2.9.3
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