drm/msm: Call shutdown conditionally

Issuing a 'reboot' command in i.MX5 leads to the following flow:

[   24.557742] [<c0769b78>] (msm_atomic_commit_tail) from [<c06db0b4>]
(commit_tail+0xa4/0x1b0)
[   24.566349] [<c06db0b4>] (commit_tail) from [<c06dbed0>]
(drm_atomic_helper_commit+0x154/0x188)
[   24.575193] [<c06dbed0>] (drm_atomic_helper_commit) from
[<c06db604>] (drm_atomic_helper_disable_all+0x154/0x1c0)
[   24.585599] [<c06db604>] (drm_atomic_helper_disable_all) from
[<c06db704>] (drm_atomic_helper_shutdown+0x94/0x12c)
[   24.596094] [<c06db704>] (drm_atomic_helper_shutdown) from

In the i.MX5 case, priv->kms is not populated (as i.MX5 does not use any
of the Qualcomm display controllers), causing a NULL pointer
dereference in msm_atomic_commit_tail():

[   24.268964] 8<--- cut here ---
[   24.274602] Unable to handle kernel NULL pointer dereference at
virtual address 00000000
[   24.283434] pgd = (ptrval)
[   24.286387] [00000000] *pgd=ca212831
[   24.290788] Internal error: Oops: 17 [#1] SMP ARM
[   24.295609] Modules linked in:
[   24.298777] CPU: 0 PID: 197 Comm: init Not tainted 5.11.0-rc2-next-20210111 torvalds#333
[   24.306276] Hardware name: Freescale i.MX53 (Device Tree Support)
[   24.312442] PC is at msm_atomic_commit_tail+0x54/0xb9c
[   24.317743] LR is at commit_tail+0xa4/0x1b0

Fix the problem by calling drm_atomic_helper_shutdown() conditionally.

Cc: <stable@vger.kernel.org>
Fixes: 9d5cbf5 ("drm/msm: add shutdown support for display platform_driver")
Suggested-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>

Author: fabioestevam

drivers/gpu/drm/msm/msm_drv.c

@@ -1311,7 +1311,8 @@ static void msm_pdev_shutdown(struct platform_device *pdev)
 {
 	struct drm_device *drm = platform_get_drvdata(pdev);
 
-	drm_atomic_helper_shutdown(drm);
+	if (get_mdp_ver(pdev))
+		drm_atomic_helper_shutdown(drm);
 }
 
 static const struct of_device_id dt_match[] = {