fbdev: mm: Deferred IO support
This implements deferred IO support in fbdev. Deferred IO is a way to delay
and repurpose IO. This implementation is done using mm's page_mkwrite and
page_mkclean hooks in order to detect, delay and then rewrite IO. This
functionality is used by hecubafb.
[adaplas]
This is useful for graphics hardware with no directly addressable/mappable
framebuffer. Implementing this will allow the "framebuffer" to be accesible
from user space via mmap().
Signed-off-by: Jaya Kumar <jayakumar.lkml@gmail.com>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/fb/deferred_io.txt b/Documentation/fb/deferred_io.txt
new file mode 100644
index 0000000..73cf9fb
--- /dev/null
+++ b/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 explaination of how one such setup
+works:
+
+- userspace app like Xfbdev mmaps framebuffer
+- deferred IO and driver sets up nopage and page_mkwrite handlers
+- userspace app tries to write to mmaped vaddress
+- we get pagefault and reach nopage handler
+- nopage 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 occuring.
+
+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);
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index 8dfa88a..61c0a03 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -91,6 +91,11 @@
blitting. This is used by drivers that don't provide their own
(accelerated) version.
+config FB_DEFERRED_IO
+ bool
+ depends on FB
+ default y
+
config FB_SVGALIB
tristate
depends on FB
diff --git a/drivers/video/Makefile b/drivers/video/Makefile
index 2814624..deb5fa5 100644
--- a/drivers/video/Makefile
+++ b/drivers/video/Makefile
@@ -20,6 +20,7 @@
obj-$(CONFIG_FB_SVGALIB) += svgalib.o
obj-$(CONFIG_FB_MACMODES) += macmodes.o
obj-$(CONFIG_FB_DDC) += fb_ddc.o
+obj-$(CONFIG_FB_DEFERRED_IO) += fb_defio.o
# Hardware specific drivers go first
obj-$(CONFIG_FB_AMIGA) += amifb.o c2p.o
diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
new file mode 100644
index 0000000..cc780f4
--- /dev/null
+++ b/drivers/video/fb_defio.c
@@ -0,0 +1,137 @@
+/*
+ * linux/drivers/video/fb_defio.c
+ *
+ * Copyright (C) 2006 Jaya Kumar
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/fb.h>
+#include <linux/list.h>
+#include <asm/uaccess.h>
+
+/* to support deferred IO */
+#include <linux/rmap.h>
+#include <linux/pagemap.h>
+
+/* this is to find and return the vmalloc-ed fb pages */
+static struct page* fb_deferred_io_nopage(struct vm_area_struct *vma,
+ unsigned long vaddr, int *type)
+{
+ unsigned long offset;
+ struct page *page;
+ struct fb_info *info = vma->vm_private_data;
+
+ offset = (vaddr - vma->vm_start) + (vma->vm_pgoff << PAGE_SHIFT);
+ if (offset >= info->fix.smem_len)
+ return NOPAGE_SIGBUS;
+
+ page = vmalloc_to_page(info->screen_base + offset);
+ if (!page)
+ return NOPAGE_OOM;
+
+ get_page(page);
+ if (type)
+ *type = VM_FAULT_MINOR;
+ return page;
+}
+
+/* vm_ops->page_mkwrite handler */
+int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
+ struct page *page)
+{
+ struct fb_info *info = vma->vm_private_data;
+ struct fb_deferred_io *fbdefio = info->fbdefio;
+
+ /* this is a callback we get when userspace first tries to
+ write to the page. we schedule a workqueue. that workqueue
+ will eventually mkclean the touched pages and execute the
+ deferred framebuffer IO. then if userspace touches a page
+ again, we repeat the same scheme */
+
+ /* protect against the workqueue changing the page list */
+ mutex_lock(&fbdefio->lock);
+ list_add(&page->lru, &fbdefio->pagelist);
+ mutex_unlock(&fbdefio->lock);
+
+ /* come back after delay to process the deferred IO */
+ schedule_delayed_work(&info->deferred_work, fbdefio->delay);
+ return 0;
+}
+
+static struct vm_operations_struct fb_deferred_io_vm_ops = {
+ .nopage = fb_deferred_io_nopage,
+ .page_mkwrite = fb_deferred_io_mkwrite,
+};
+
+static int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
+{
+ vma->vm_ops = &fb_deferred_io_vm_ops;
+ vma->vm_flags |= ( VM_IO | VM_RESERVED | VM_DONTEXPAND );
+ vma->vm_private_data = info;
+ return 0;
+}
+
+/* workqueue callback */
+static void fb_deferred_io_work(struct work_struct *work)
+{
+ struct fb_info *info = container_of(work, struct fb_info,
+ deferred_work.work);
+ struct list_head *node, *next;
+ struct page *cur;
+ struct fb_deferred_io *fbdefio = info->fbdefio;
+
+ /* here we mkclean the pages, then do all deferred IO */
+ mutex_lock(&fbdefio->lock);
+ list_for_each_entry(cur, &fbdefio->pagelist, lru) {
+ lock_page(cur);
+ page_mkclean(cur);
+ unlock_page(cur);
+ }
+
+ /* driver's callback with pagelist */
+ fbdefio->deferred_io(info, &fbdefio->pagelist);
+
+ /* clear the list */
+ list_for_each_safe(node, next, &fbdefio->pagelist) {
+ list_del(node);
+ }
+ mutex_unlock(&fbdefio->lock);
+}
+
+void fb_deferred_io_init(struct fb_info *info)
+{
+ struct fb_deferred_io *fbdefio = info->fbdefio;
+
+ BUG_ON(!fbdefio);
+ mutex_init(&fbdefio->lock);
+ info->fbops->fb_mmap = fb_deferred_io_mmap;
+ INIT_DELAYED_WORK(&info->deferred_work, fb_deferred_io_work);
+ INIT_LIST_HEAD(&fbdefio->pagelist);
+ if (fbdefio->delay == 0) /* set a default of 1 s */
+ fbdefio->delay = HZ;
+}
+EXPORT_SYMBOL_GPL(fb_deferred_io_init);
+
+void fb_deferred_io_cleanup(struct fb_info *info)
+{
+ struct fb_deferred_io *fbdefio = info->fbdefio;
+
+ BUG_ON(!fbdefio);
+ cancel_delayed_work(&info->deferred_work);
+ flush_scheduled_work();
+}
+EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
+
+MODULE_LICENSE("GPL");
diff --git a/include/linux/fb.h b/include/linux/fb.h
index be913ec..8a8255b 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -561,6 +561,16 @@
void (*readio) (struct fb_info *info, void *dst, void __iomem *src, unsigned int size);
};
+#ifdef CONFIG_FB_DEFERRED_IO
+struct fb_deferred_io {
+ /* delay between mkwrite and deferred handler */
+ unsigned long delay;
+ struct mutex lock; /* mutex that protects the page list */
+ struct list_head pagelist; /* list of touched pages */
+ /* callback */
+ void (*deferred_io)(struct fb_info *info, struct list_head *pagelist);
+};
+#endif
/*
* Frame buffer operations
@@ -778,6 +788,10 @@
struct mutex bl_curve_mutex;
u8 bl_curve[FB_BACKLIGHT_LEVELS];
#endif
+#ifdef CONFIG_FB_DEFERRED_IO
+ struct delayed_work deferred_work;
+ struct fb_deferred_io *fbdefio;
+#endif
struct fb_ops *fbops;
struct device *device; /* This is the parent */
@@ -913,6 +927,12 @@
}
}
+#ifdef CONFIG_FB_DEFERRED_IO
+/* drivers/video/fb_defio.c */
+extern void fb_deferred_io_init(struct fb_info *info);
+extern void fb_deferred_io_cleanup(struct fb_info *info);
+#endif
+
/* drivers/video/fbsysfs.c */
extern struct fb_info *framebuffer_alloc(size_t size, struct device *dev);
extern void framebuffer_release(struct fb_info *info);
diff --git a/mm/rmap.c b/mm/rmap.c
index 75a32be..304f519 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -505,6 +505,7 @@
return ret;
}
+EXPORT_SYMBOL_GPL(page_mkclean);
/**
* page_set_anon_rmap - setup new anonymous rmap
