Nvidia driver 390.87 patches needed for Linux RT kernel and related to the install method described here http://linuxaudioproduction.blogspot.com/2015/09/how-to-patching-and-compiling-nvidia.html

nv-linux.h_rt.patch

--- nv-linux.h.bak	2018-12-30 11:31:22.677374865 +0100
+++ nv-linux.h	2018-12-30 11:35:16.447873828 +0100
@@ -43,6 +43,8 @@
 #include <linux/version.h>
 #include <linux/utsname.h>
 
+#define CONFIG_PREEMPT_RT_FULL 1
+
 #if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 9)
 #error "This driver does not support kernels older than 2.6.9!"
 #elif LINUX_VERSION_CODE < KERNEL_VERSION(2, 7, 0)
@@ -361,10 +363,6 @@
 #endif
 #endif
 
-#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_PREEMPT_RT_FULL)
-#define NV_CONFIG_PREEMPT_RT 1
-#endif
-
 #if defined(NVCPU_X86)
 #ifndef write_cr4
 #define write_cr4(x) __asm__ ("movl %0,%%cr4" :: "r" (x));

nv-lock.h_rt.patch

--- nv-lock.h.bak	2018-12-30 11:31:31.841314906 +0100
+++ nv-lock.h	2018-12-30 11:35:57.527615218 +0100
@@ -21,7 +21,9 @@
 #include <asm/semaphore.h>
 #endif
 
-#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_PREEMPT_RT_FULL)
+#define CONFIG_PREEMPT_RT_FULL 1
+
+#if defined(CONFIG_PREEMPT_RT_FULL)
 typedef raw_spinlock_t            nv_spinlock_t;
 #define NV_SPIN_LOCK_INIT(lock)   raw_spin_lock_init(lock)
 #define NV_SPIN_LOCK_IRQ(lock)    raw_spin_lock_irq(lock)
@@ -43,7 +45,7 @@
 #define NV_SPIN_UNLOCK_WAIT(lock) spin_unlock_wait(lock)
 #endif
 
-#if defined(NV_CONFIG_PREEMPT_RT)
+#if defined(CONFIG_PREEMPT_RT_FULL)
 #define NV_INIT_SEMA(sema, val) sema_init(sema,val)
 #else
 #if !defined(__SEMAPHORE_INITIALIZER) && defined(__COMPAT_SEMAPHORE_INITIALIZER)