[PATCH 1/3] uio: Allow handling of non page-aligned memory regions

[Michal Sojka]

Since commit b65502879556 ("uio: we cannot mmap unaligned page
contents") addresses and sizes of UIO memory regions must be
page-aligned. If the address in the BAR register is not page-aligned,
the mentioned commit forces the UIO driver to round the address down
to the page size. Then, there is no easy way for user-space to learn
the offset of the actual memory region within the page, because the
offset seen in the sysfs is calculated from the rounded address and
thus it is always zero.

Fix that problem by including the offset in struct uio_mem. UIO
drivers can set this field and its value is reported via sysfs.

Drivers for hardware with page-aligned BARs need not to be modified
provided that they initialize struct uio_info with zeros.

Signed-off-by: Michal Sojka <sojkam1@xxxxxxxxxxx>
---
 drivers/uio/uio.c          |  2 +-
 include/linux/uio_driver.h | 13 ++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index fba021f5736a..27c329131350 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -66,7 +66,7 @@ static ssize_t map_size_show(struct uio_mem *mem, char *buf)
 
 static ssize_t map_offset_show(struct uio_mem *mem, char *buf)
 {
-	return sprintf(buf, "0x%llx\n", (unsigned long long)mem->addr & ~PAGE_MASK);
+	return sprintf(buf, "0x%llx\n", (unsigned long long)mem->offs);
 }
 
 struct map_sysfs_entry {
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 32c0e83d6239..89b53094f127 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -23,11 +23,13 @@ struct uio_map;
 /**
  * struct uio_mem - description of a UIO memory region
  * @name:		name of the memory region for identification
- * @addr:		address of the device's memory (phys_addr is used since
- * 			addr can be logical, virtual, or physical & phys_addr_t
- * 			should always be large enough to handle any of the
- * 			address types)
- * @size:		size of IO
+ * @addr:               address of the device's memory rounded to page
+ * 			size (phys_addr is used since addr can be
+ * 			logical, virtual, or physical & phys_addr_t
+ * 			should always be large enough to handle any of
+ * 			the address types)
+ * @offs:               offset of device memory within the page
+ * @size:		size of IO (multiple of page size)
  * @memtype:		type of memory addr points to
  * @internal_addr:	ioremap-ped version of addr, for driver internal use
  * @map:		for use by the UIO core only.
@@ -35,6 +37,7 @@ struct uio_map;
 struct uio_mem {
 	const char		*name;
 	phys_addr_t		addr;
+	unsigned long		offs;;
 	resource_size_t		size;
 	int			memtype;
 	void __iomem		*internal_addr;
-- 
2.11.0