drm/i915: fix freeze with blank screen booting highmem

x86_64 boots and displays fine, but booting x86_32 with CONFIG_HIGHMEM
has frozen with a blank screen throughout 3.16-rc on this ThinkPad T420s,
with i915 generation 6 graphics.

Fix 9d0a6fa6c5e6 ("drm/i915: add render state initialization"): kunmap()
takes struct page * argument, not virtual address.  Which the compiler
kindly points out, if you use the appropriate u32 *batch, instead of
silencing it with a void *.

Why did bisection lead decisively to nearby 229b0489aa75 ("drm/i915:
add null render states for gen6, gen7 and gen8")?  Because the u32
deposited at that virtual address by the previous stub failed the
PageHighMem test, and so did no harm.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/i915_gem_render_state.c b/drivers/gpu/drm/i915/i915_gem_render_state.c
index 3521f998a1788488b8c396860f6433ffacb81ae2..34894b57306401645a2184d48d99ed2966c8c9f1 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_render_state.c
+++ b/drivers/gpu/drm/i915/i915_gem_render_state.c
@@ -31,7 +31,7 @@
 struct i915_render_state {
        struct drm_i915_gem_object *obj;
        unsigned long ggtt_offset;
-       void *batch;
+       u32 *batch;
        u32 size;
        u32 len;
 };
@@ -80,7 +80,7 @@ free:
 
 static void render_state_free(struct i915_render_state *so)
 {
-       kunmap(so->batch);
+       kunmap(kmap_to_page(so->batch));
        i915_gem_object_ggtt_unpin(so->obj);
        drm_gem_object_unreference(&so->obj->base);
        kfree(so);