commonlib: provide incoherent region device

The MRC cache uses an incoherent mechanism for updating the
cache contents in that it assumes memory mapped boot device
access for checking against latest data for update. However,
it uses another driver for updating the underlying storage
area.

In order to aid in moving the MRC cache over to using
region_devices for updates provide an implementation of
a region_device which performs reads and writes to different
region_devices so that different drivers can be used
transparently.

BUG=chrome-os-partner:56151

Change-Id: I30e858245c30cbccd6313aff5ebecd3fd98d7302
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/17716
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/commonlib/include/commonlib/region.h b/src/commonlib/include/commonlib/region.h
index bc3ded1d0a..3f7d3bd52f 100644
--- a/src/commonlib/include/commonlib/region.h
+++ b/src/commonlib/include/commonlib/region.h
@@ -245,4 +245,27 @@ void xlate_region_device_rw_init(struct xlate_region_device *xdev,
 			      size_t sub_offset, size_t sub_size,
 			      size_t parent_size);
 
+/* This type can be used for incoherent access where the read and write
+ * operations are backed by separate drivers. An example is x86 systems
+ * with memory mapped media for reading but use a spi flash driver for
+ * writing. One needs to ensure using this object is appropriate in context. */
+struct incoherent_rdev {
+	struct region_device rdev;
+	const struct region_device *read;
+	const struct region_device *write;
+};
+
+/* Initialize an incoherent_rdev based on the region as well as the read and
+ * write rdevs. The read and write rdevs should match in size to the passed
+ * in region. If not the initialization will fail returning NULL. Otherwise
+ * the function will return a pointer to the containing region_device to
+ * be used for region operations. Therefore, the lifetime of the returned
+ * pointer matches the lifetime of the incoherent_rdev object. Likewise,
+ * the lifetime of the read and write rdev need to match the lifetime of
+ * the incoherent_rdev object. */
+const struct region_device *incoherent_rdev_init(struct incoherent_rdev *irdev,
+				const struct region *r,
+				const struct region_device *read,
+				const struct region_device *write);
+
 #endif /* _REGION_H_ */