fbdev: add mutex for fb_mmap locking

Add a mutex to avoid a circular locking problem between the mm layer
semaphore and fbdev ioctl mutex through the fb_mmap() call.

Also, add mutex to all places where smem_start and smem_len fields change
so the mutex inside the fb_mmap() is actually used.  Changing of these
fields before calling the framebuffer_register() are not mutexed.

This is 2.6.31 material.  It removes one lockdep (fb_mmap() and
register_framebuffer()) but there is still another one (fb_release() and
register_framebuffer()).  It also cleans up handling of the smem_start and
smem_len fields used by mutexed section of the fb_mmap().

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 13 deletions

diff --git a/drivers/video/sh7760fb.c b/drivers/video/sh7760fb.c
index 653bdfee3057..9f6d6e61f0cc 100644
--- a/drivers/video/sh7760fb.c
+++ b/drivers/video/sh7760fb.c
@@ -120,18 +120,6 @@ static int sh7760_setcolreg (u_int regno,
         return 0;
 }
 
-static void encode_fix(struct fb_fix_screeninfo *fix, struct fb_info *info,
-                       unsigned long stride)
-{
-        memset(fix, 0, sizeof(struct fb_fix_screeninfo));
-        strcpy(fix->id, "sh7760-lcdc");
-
-        fix->smem_start = (unsigned long)info->screen_base;
-        fix->smem_len = info->screen_size;
-
-        fix->line_length = stride;
-}
-
 static int sh7760fb_get_color_info(struct device *dev,
                                    u16 lddfr, int *bpp, int *gray)
 {
@@ -334,7 +322,8 @@ static int sh7760fb_set_par(struct fb_info *info)
 
         iowrite32(ldsarl, par->base + LDSARL);  /* mem for lower half of DSTN */
 
-        encode_fix(&info->fix, info, stride);
+        info->fix.line_length = stride;
+
         sh7760fb_check_var(&info->var, info);
 
         sh7760fb_blank(FB_BLANK_UNBLANK, info); /* panel on! */
@@ -435,6 +424,8 @@ static int sh7760fb_alloc_mem(struct fb_info *info)
 
         info->screen_base = fbmem;
         info->screen_size = vram;
+        info->fix.smem_start = (unsigned long)info->screen_base;
+        info->fix.smem_len = info->screen_size;
 
         return 0;
 }
@@ -520,6 +511,8 @@ static int __devinit sh7760fb_probe(struct platform_device *pdev)
         info->var.transp.length = 0;
         info->var.transp.msb_right = 0;
 
+        strcpy(info->fix.id, "sh7760-lcdc");
+
         /* set the DON2 bit now, before cmap allocation, as it will randomize
          * palette memory.
          */