drm/gma500: Add driver private mutex for the fault handler

There's currently two places where the gma500 fault handler relies
upon dev->struct_mutex:
- To protect r->mappping
- To make sure vm_insert_pfn isn't called concurrently (in which case
  the 2nd thread would get an error code).

Everything else (specifically psb_gtt_pin) is already protected by
some other locks. Hence just create a new driver-private mmap_mutex
just for this function.

With this gma500 is complete dev->struct_mutex free!

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448271183-20523-21-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/gma500/gem.c

@@ -182,7 +182,7 @@ int psb_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 
 	/* Make sure we don't parallel update on a fault, nor move or remove
 	   something from beneath our feet */
-	mutex_lock(&dev->struct_mutex);
+	mutex_lock(&dev_priv->mmap_mutex);
 
 	/* For now the mmap pins the object and it stays pinned. As things
 	   stand that will do us no harm */
@@ -208,7 +208,7 @@ int psb_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	ret = vm_insert_pfn(vma, (unsigned long)vmf->virtual_address, pfn);
 
 fail:
-	mutex_unlock(&dev->struct_mutex);
+	mutex_unlock(&dev_priv->mmap_mutex);
 	switch (ret) {
 	case 0:
 	case -ERESTARTSYS:

drivers/gpu/drm/gma500/gtt.c

@@ -425,6 +425,7 @@ int psb_gtt_init(struct drm_device *dev, int resume)
 
 	if (!resume) {
 		mutex_init(&dev_priv->gtt_mutex);
+		mutex_init(&dev_priv->mmap_mutex);
 		psb_gtt_alloc(dev);
 	}
 

drivers/gpu/drm/gma500/psb_drv.h

@@ -465,6 +465,8 @@ struct drm_psb_private {
 	struct mutex gtt_mutex;
 	struct resource *gtt_mem;	/* Our PCI resource */
 
+	struct mutex mmap_mutex;
+
 	struct psb_mmu_driver *mmu;
 	struct psb_mmu_pd *pf_pd;