Add the rt linux 4.1.3-rt3 as base

Import the rt linux 4.1.3-rt3 as OPNFV kvm base.

It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and
the base is:

commit 0917f823c59692d751951bf5ea699a2d1e2f26a2
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date:   Sat Jul 25 12:13:34 2015 +0200

    Prepare v4.1.3-rt3

    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

We lose all the git history this way and it's not good. We
should apply another opnfv project repo in future.

Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423
Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com>

1 files changed, 75 insertions, 0 deletions

diff --git a/kernel/Documentation/fb/deferred_io.txt b/kernel/Documentation/fb/deferred_io.txt
new file mode 100644
index 000000000..748328370
--- /dev/null
+++ b/kernel/Documentation/fb/deferred_io.txt
@@ -0,0 +1,75 @@
+Deferred IO
+-----------
+
+Deferred IO is a way to delay and repurpose IO. It uses host memory as a
+buffer and the MMU pagefault as a pretrigger for when to perform the device
+IO. The following example may be a useful explanation of how one such setup
+works:
+
+- userspace app like Xfbdev mmaps framebuffer
+- deferred IO and driver sets up fault and page_mkwrite handlers
+- userspace app tries to write to mmaped vaddress
+- we get pagefault and reach fault handler
+- fault handler finds and returns physical page
+- we get page_mkwrite where we add this page to a list
+- schedule a workqueue task to be run after a delay
+- app continues writing to that page with no additional cost. this is
+  the key benefit.
+- the workqueue task comes in and mkcleans the pages on the list, then
+ completes the work associated with updating the framebuffer. this is
+  the real work talking to the device.
+- app tries to write to the address (that has now been mkcleaned)
+- get pagefault and the above sequence occurs again
+
+As can be seen from above, one benefit is roughly to allow bursty framebuffer
+writes to occur at minimum cost. Then after some time when hopefully things
+have gone quiet, we go and really update the framebuffer which would be
+a relatively more expensive operation.
+
+For some types of nonvolatile high latency displays, the desired image is
+the final image rather than the intermediate stages which is why it's okay
+to not update for each write that is occurring.
+
+It may be the case that this is useful in other scenarios as well. Paul Mundt
+has mentioned a case where it is beneficial to use the page count to decide
+whether to coalesce and issue SG DMA or to do memory bursts.
+
+Another one may be if one has a device framebuffer that is in an usual format,
+say diagonally shifting RGB, this may then be a mechanism for you to allow
+apps to pretend to have a normal framebuffer but reswizzle for the device
+framebuffer at vsync time based on the touched pagelist.
+
+How to use it: (for applications)
+---------------------------------
+No changes needed. mmap the framebuffer like normal and just use it.
+
+How to use it: (for fbdev drivers)
+----------------------------------
+The following example may be helpful.
+
+1. Setup your structure. Eg:
+
+static struct fb_deferred_io hecubafb_defio = {
+	.delay		= HZ,
+	.deferred_io	= hecubafb_dpy_deferred_io,
+};
+
+The delay is the minimum delay between when the page_mkwrite trigger occurs
+and when the deferred_io callback is called. The deferred_io callback is
+explained below.
+
+2. Setup your deferred IO callback. Eg:
+static void hecubafb_dpy_deferred_io(struct fb_info *info,
+				struct list_head *pagelist)
+
+The deferred_io callback is where you would perform all your IO to the display
+device. You receive the pagelist which is the list of pages that were written
+to during the delay. You must not modify this list. This callback is called
+from a workqueue.
+
+3. Call init
+	info->fbdefio = &hecubafb_defio;
+	fb_deferred_io_init(info);
+
+4. Call cleanup
+	fb_deferred_io_cleanup(info);