[RFC][PATCH 1/2] uio: allow drivers to override the pgprot for mmap

[Kumar Gala <galak@kernel.crashing.org>]

For some devices, the default behavior of pgprot_noncached() is not
appropriate for all of its mappable regions. This provides a means for
the kernel side of the UIO driver to override the flags without having
to implement its own full mmap callback.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Geoff Thorpe <geoff@geoffthorpe.net>
---
 drivers/uio/uio.c          |    6 +++++-
 include/linux/uio_driver.h |    3 +++
 2 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index dc27d89..0aebe27 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -655,7 +655,11 @@ static int uio_mmap_physical(struct vm_area_struct *vma)
 
 	vma->vm_flags |= VM_IO | VM_RESERVED;
 
-	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+	if (idev->info->set_pgprot)
+		vma->vm_page_prot = idev->info->set_pgprot(idev->info, mi,
+							   vma->vm_page_prot);
+	else
+		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 
 	return remap_pfn_range(vma,
 			       vma->vm_start,
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index fd99ff9..edfe7c8 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -80,6 +80,7 @@ struct uio_device;
  * @open:		open operation for this uio device
  * @release:		release operation for this uio device
  * @irqcontrol:		disable/enable irqs when 0/1 is written to /dev/uioX
+ * @set_pgprot:		allow driver to override default(noncached) pgprot
  */
 struct uio_info {
 	struct uio_device	*uio_dev;
@@ -95,6 +96,8 @@ struct uio_info {
 	int (*open)(struct uio_info *info, struct inode *inode);
 	int (*release)(struct uio_info *info, struct inode *inode);
 	int (*irqcontrol)(struct uio_info *info, s32 irq_on);
+	pgprot_t (*set_pgprot)(struct uio_info *uio, unsigned int mem_idx,
+			       pgprot_t prot);
 };
 
 extern int __must_check
-- 
1.7.3.4