From: Matthew Garrett What ---- The following patch adds a state file to /sys/class/graphics/fb*. Echoing values to it will alter the contents of fb_info->state, resulting in reads and writes to the framebuffer device being discarded and EPERM being returned. Why --- When resuming from ACPI suspend to RAM, video hardware is not required to be in a sane state. The most effective workaround is vbetool, a userspace application that executes video BIOS code in order to reinitialise the graphics hardware. Different hardware requires sensible than putting it in the kernel. However, since reinitialisation occurs in userspace, it happens some time after the kernel has restarted. During resume, the kernel attempts to printk all sorts of information. If a framebuffer is in use, this will trigger framebuffer writes. Since the hardware has not yet been reinitialised, this can result in system hangs. This patch allows userspace to disable framebuffer writes immediately before suspend. On resume, userspace can then reinitialise the hardware and reenable framebuffer writes. As a result, system resiliance over suspend/resume is improved. Signed-off-by: Matthew Garrett Cc: "Antonino A. Daplas" Signed-off-by: Andrew Morton --- drivers/video/fbsysfs.c | 25 +++++++++++++++++++++++++ 1 files changed, 25 insertions(+) diff -puN drivers/video/fbsysfs.c~add-sysfs-entry-to-disable-framebuffer-access drivers/video/fbsysfs.c --- devel/drivers/video/fbsysfs.c~add-sysfs-entry-to-disable-framebuffer-access 2005-11-26 20:25:34.000000000 -0800 +++ devel-akpm/drivers/video/fbsysfs.c 2005-11-26 20:25:34.000000000 -0800 @@ -492,6 +492,30 @@ static ssize_t show_name(struct class_de return snprintf(buf, PAGE_SIZE, "%s\n", fb_info->fix.id); } +static ssize_t store_fbstate(struct class_device *class_device, const char * buf, + size_t count) +{ + struct fb_info *fb_info = + (struct fb_info *)class_get_devdata(class_device); + u32 state; + char *last = NULL; + + state = simple_strtoul(buf, &last, 0); + + acquire_console_sem(); + fb_set_suspend(fb_info, (int)state); + release_console_sem(); + + return count; +} + +static ssize_t show_fbstate(struct class_device *class_device, char *buf) +{ + struct fb_info *fb_info = + (struct fb_info *)class_get_devdata(class_device); + return snprintf(buf, PAGE_SIZE, "%d\n", fb_info->state); +} + static struct class_device_attribute class_device_attrs[] = { __ATTR(bits_per_pixel, S_IRUGO|S_IWUSR, show_bpp, store_bpp), __ATTR(blank, S_IRUGO|S_IWUSR, show_blank, store_blank), @@ -507,6 +531,7 @@ static struct class_device_attribute cla __ATTR(rotate, S_IRUGO|S_IWUSR, show_rotate, store_rotate), __ATTR(con_rotate, S_IRUGO|S_IWUSR, show_con_rotate, store_con_rotate), __ATTR(con_rotate_all, S_IWUSR, NULL, store_con_rotate_all), + __ATTR(state, S_IRUGO|S_IWUSR, show_fbstate, store_fbstate), }; int fb_init_class_device(struct fb_info *fb_info) _