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>

1 files changed, 137 insertions, 0 deletions

diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
new file mode 100644
index 000000000000..cc780f4e183d
--- /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");