Currently we are allocating drm_device in rockchip_drm_bind, so if the
suspend/resume code access it when drm is not bound, we would hit this
crash:

[  253.402836] Unable to handle kernel NULL pointer dereference at virtual 
address 00000028
[  253.402837] pgd = ffffffc06c9b0000
[  253.402841] [00000028] *pgd=0000000000000000, *pud=0000000000000000
[  253.402844] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[  253.402859] Modules linked in: btusb btrtl btbcm btintel bluetooth 
ath10k_pci ath10k_core ar10k_ath ar10k_mac80211 cfg80211 ip6table_filter asix 
usbnet mii
[  253.402864] CPU: 4 PID: 1331 Comm: cat Not tainted 4.4.70 #15
[  253.402865] Hardware name: Google Scarlet (DT)
[  253.402867] task: ffffffc076c0ce00 ti: ffffffc06c2c8000 task.ti: 
ffffffc06c2c8000
[  253.402871] PC is at rockchip_drm_sys_suspend+0x20/0x5c

Add sanity checks to prevent that.

Reported-by: Brian Norris <briannor...@chromium.com>
Signed-off-by: Jeffy Chen <jeffy.c...@rock-chips.com>

---

 drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c 
b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
index c41f48a..ff3d0f5 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
@@ -270,11 +270,15 @@ static void rockchip_drm_fb_resume(struct drm_device *drm)
 static int rockchip_drm_sys_suspend(struct device *dev)
 {
        struct drm_device *drm = dev_get_drvdata(dev);
-       struct rockchip_drm_private *priv = drm->dev_private;
+       struct rockchip_drm_private *priv;
+
+       if (!drm)
+               return 0;
 
        drm_kms_helper_poll_disable(drm);
        rockchip_drm_fb_suspend(drm);
 
+       priv = drm->dev_private;
        priv->state = drm_atomic_helper_suspend(drm);
        if (IS_ERR(priv->state)) {
                rockchip_drm_fb_resume(drm);
@@ -288,8 +292,12 @@ static int rockchip_drm_sys_suspend(struct device *dev)
 static int rockchip_drm_sys_resume(struct device *dev)
 {
        struct drm_device *drm = dev_get_drvdata(dev);
-       struct rockchip_drm_private *priv = drm->dev_private;
+       struct rockchip_drm_private *priv;
+
+       if (!drm)
+               return 0;
 
+       priv = drm->dev_private;
        drm_atomic_helper_resume(drm, priv->state);
        rockchip_drm_fb_resume(drm);
        drm_kms_helper_poll_enable(drm);
-- 
2.1.4


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