gpu: nvgpu: fix MISRA 21.6 violation in nvgpu.common.mm.as

Below MISRA 21.6 violation is reported in nvgpu.common.mm.as

${TEGRA_TOP}/kernel/nvgpu/drivers/gpu/nvgpu/common/mm/as.c:79:
misra_violation: Using function "snprintf".

Fix this by replacing snprintf with strncpy.
Add nvgpu_strnadd_u32 function to convert u32 to string
The function supports radix from 2 to 16.

Jira NVGPU-3333

Change-Id: Idee739dfdedeabb74d0d9f7d4cddd798445f0ee1
Signed-off-by: Thomas Fleury <tfleury@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2117019
GVS: Gerrit_Virtual_Submit
Reviewed-by: Philip Elcan <pelcan@nvidia.com>
Reviewed-by: Vaibhav Kachore <vkachore@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/common/mm/as.c

@@ -28,6 +28,7 @@
 #include <nvgpu/vm.h>
 #include <nvgpu/log2.h>
 #include <nvgpu/gk20a.h>
+#include <nvgpu/string.h>
 
 /* dumb allocator... */
 static int generate_as_share_id(struct gk20a_as *as)
@@ -55,6 +56,7 @@ static int gk20a_vm_alloc_share(struct gk20a_as_share *as_share,
 	struct mm_gk20a *mm = &g->mm;
 	struct vm_gk20a *vm;
 	char name[32];
+	char *p;
 	const bool userspace_managed =
 		(flags & NVGPU_AS_ALLOC_USERSPACE_MANAGED) != 0U;
 	const bool unified_va =
@@ -76,7 +78,8 @@ static int gk20a_vm_alloc_share(struct gk20a_as_share *as_share,
 		}
 	}
 
-	(void) snprintf(name, sizeof(name), "as_%d", as_share->id);
+	p = strncpy(name, "as_", sizeof(name) - 1);
+	(void) nvgpu_strnadd_u32(p, as_share->id, sizeof(name) - (p-name), 10U);
 
 	vm = nvgpu_vm_init(g, big_page_size,
 			   U64(big_page_size) << U64(10),

drivers/gpu/nvgpu/common/string.c

@@ -21,6 +21,7 @@
  */
 
 #include <nvgpu/string.h>
+#include <nvgpu/log.h>
 
 void
 nvgpu_memcpy(u8 *destb, const u8 *srcb, size_t n)
@@ -33,3 +34,46 @@ nvgpu_memcmp(const u8 *b1, const u8 *b2, size_t n)
 {
 	return memcmp(b1, b2, n);
 }
+
+int nvgpu_strnadd_u32(char *dst, const u32 value, size_t size, u32 radix)
+{
+	int n;
+	u32 v;
+	char *p;
+	u32 digit;
+
+	if (radix < 2U || radix > 16U) {
+		return 0;
+	}
+
+	/* how many digits do we need ? */
+	n = 0;
+	v = value;
+	do {
+		n++;
+		v = v / radix;
+	} while (v > 0U);
+
+	/* bail out if there is not room for '\0' */
+	if (n >= (int)size) {
+		return 0;
+	}
+
+	/* number of digits (not including '\0') */
+	p = dst + n;
+
+	/* terminate with '\0' */
+	*p = '\0';
+	p--;
+
+	v = value;
+	do {
+		digit = v % radix;
+		*p = "0123456789abdcef"[digit];
+		v = v / radix;
+		p--;
+	}
+	while (v > 0U);
+
+	return n;
+}

drivers/gpu/nvgpu/include/nvgpu/string.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2018-2019, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -54,4 +54,13 @@ void nvgpu_memcpy(u8 *destb, const u8 *srcb, size_t n);
  */
 int nvgpu_memcmp(const u8 *b1, const u8 *b2, size_t n);
 
+/**
+ * nvgpu_strnadd_u32 - formats u32 into null-terminated string
+ *
+ * Returns number of digits added to string (not including '\0')
+ * Returns 0 in case of invalid dst or radix, or insufficient space.
+ * Returns 0 if there was no room to add '\0'
+ */
+int nvgpu_strnadd_u32(char *dst, const u32 value, size_t size, u32 radix);
+
 #endif /* NVGPU_STRING_H */