diff options
| -rw-r--r-- | Documentation/fb/deferred_io.txt | 75 | ||||
| -rw-r--r-- | drivers/video/Kconfig | 5 | ||||
| -rw-r--r-- | drivers/video/Makefile | 1 | ||||
| -rw-r--r-- | drivers/video/fb_defio.c | 137 | ||||
| -rw-r--r-- | include/linux/fb.h | 20 | ||||
| -rw-r--r-- | mm/rmap.c | 1 |
6 files changed, 239 insertions, 0 deletions
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 @@ config FB_CFB_IMAGEBLIT 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-$(CONFIG_FB_CFB_IMAGEBLIT) += cfbimgblt.o obj-$(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 @@ struct fb_pixmap { 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 fb_info { 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 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch, } } +#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); @@ -505,6 +505,7 @@ int page_mkclean(struct page *page) return ret; } +EXPORT_SYMBOL_GPL(page_mkclean); /** * page_set_anon_rmap - setup new anonymous rmap |