libfdt: Introduce fdt_create_with_flags()

There is a need to be able to specify some options when building an FDT
with the SW interface. This can be accomplished with minimal changes by
storing intermediate data in the fdt header itself, in fields that are
not otherwise needed during the creation process and can be set by
fdt_finish().

The fdt.magic field is already used exactly this way, as a state to
check with callers that the FDT has been created but not yet finished.

fdt.version and fdt.last_comp_version are used to make room for more
intermediate state. These are adjacent and unused during the building
process. last_comp_version is not yet used for intermediate state, but
it is zeroed and treated as used, so as to allow future growth easily.

A new interface, fdt_create_with_flags() is added, which takes 32-bit
flag value to control creation.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-Id: <20190509094122.834-3-npiggin@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

3 files changed, 66 insertions, 3 deletions

diff --git a/cpukit/dtc/libfdt/fdt_strerror.c b/cpukit/dtc/libfdt/fdt_strerror.c
index 9677a1887e..0e6b4fd5e7 100644
--- a/cpukit/dtc/libfdt/fdt_strerror.c
+++ b/cpukit/dtc/libfdt/fdt_strerror.c
@@ -82,6 +82,7 @@ static struct fdt_errtabent fdt_errtable[] = {
 	FDT_ERRTABENT(FDT_ERR_BADVALUE),
 	FDT_ERRTABENT(FDT_ERR_BADOVERLAY),
 	FDT_ERRTABENT(FDT_ERR_NOPHANDLES),
+	FDT_ERRTABENT(FDT_ERR_BADFLAGS),
 };
 #define FDT_ERRTABSIZE	(sizeof(fdt_errtable) / sizeof(fdt_errtable[0]))
 
diff --git a/cpukit/dtc/libfdt/fdt_sw.c b/cpukit/dtc/libfdt/fdt_sw.c
index 113f28ad3f..ba05868845 100644
--- a/cpukit/dtc/libfdt/fdt_sw.c
+++ b/cpukit/dtc/libfdt/fdt_sw.c
@@ -121,6 +121,12 @@ static int fdt_sw_probe_struct_(void *fdt)
 			return err; \
 	}
 
+static inline uint32_t sw_flags(void *fdt)
+{
+	/* assert: (fdt_magic(fdt) == FDT_SW_MAGIC) */
+	return fdt_last_comp_version(fdt);
+}
+
 /* 'complete' state:	Enter this state after fdt_finish()
  *
  * Allowed functions: none
@@ -141,7 +147,7 @@ static void *fdt_grab_space_(void *fdt, size_t len)
 	return fdt_offset_ptr_w_(fdt, offset);
 }
 
-int fdt_create(void *buf, int bufsize)
+int fdt_create_with_flags(void *buf, int bufsize, uint32_t flags)
 {
 	const size_t hdrsize = FDT_ALIGN(sizeof(struct fdt_header),
 					 sizeof(struct fdt_reserve_entry));
@@ -150,11 +156,22 @@ int fdt_create(void *buf, int bufsize)
 	if (bufsize < hdrsize)
 		return -FDT_ERR_NOSPACE;
 
+	if (flags & ~FDT_CREATE_FLAGS_ALL)
+		return -FDT_ERR_BADFLAGS;
+
 	memset(buf, 0, bufsize);
 
+	/*
+	 * magic and last_comp_version keep intermediate state during the fdt
+	 * creation process, which is replaced with the proper FDT format by
+	 * fdt_finish().
+	 *
+	 * flags should be accessed with sw_flags().
+	 */
 	fdt_set_magic(fdt, FDT_SW_MAGIC);
 	fdt_set_version(fdt, FDT_LAST_SUPPORTED_VERSION);
-	fdt_set_last_comp_version(fdt, FDT_FIRST_SUPPORTED_VERSION);
+	fdt_set_last_comp_version(fdt, flags);
+
 	fdt_set_totalsize(fdt,  bufsize);
 
 	fdt_set_off_mem_rsvmap(fdt, hdrsize);
@@ -164,6 +181,11 @@ int fdt_create(void *buf, int bufsize)
 	return 0;
 }
 
+int fdt_create(void *buf, int bufsize)
+{
+	return fdt_create_with_flags(buf, bufsize, 0);
+}
+
 int fdt_resize(void *fdt, void *buf, int bufsize)
 {
 	size_t headsize, tailsize;
@@ -377,6 +399,10 @@ int fdt_finish(void *fdt)
 
 	/* Finally, adjust the header */
 	fdt_set_totalsize(fdt, newstroffset + fdt_size_dt_strings(fdt));
+
+	/* And fix up fields that were keeping intermediate state. */
+	fdt_set_last_comp_version(fdt, FDT_FIRST_SUPPORTED_VERSION);
 	fdt_set_magic(fdt, FDT_MAGIC);
+
 	return 0;
 }
diff --git a/cpukit/include/libfdt.h b/cpukit/include/libfdt.h
index 1f44177f34..c2dee3eaa6 100644
--- a/cpukit/include/libfdt.h
+++ b/cpukit/include/libfdt.h
@@ -138,7 +138,11 @@
 	/* FDT_ERR_NOPHANDLES: The device tree doesn't have any
 	 * phandle available anymore without causing an overflow */
 
-#define FDT_ERR_MAX		17
+#define FDT_ERR_BADFLAGS	18
+	/* FDT_ERR_BADFLAGS: The function was passed a flags field that
+	 * contains invalid flags or an invalid combination of flags. */
+
+#define FDT_ERR_MAX		18
 
 /* constants */
 #define FDT_MAX_PHANDLE 0xfffffffe
@@ -1429,7 +1433,39 @@ int fdt_nop_node(void *fdt, int nodeoffset);
 /* Sequential write functions                                         */
 /**********************************************************************/
 
+#define FDT_CREATE_FLAGS_ALL	0
+
+/**
+ * fdt_create_with_flags - begin creation of a new fdt
+ * @fdt: pointer to memory allocated where fdt will be created
+ * @bufsize: size of the memory space at fdt
+ * @flags: a valid combination of FDT_CREATE_FLAG_ flags, or 0.
+ *
+ * fdt_create_with_flags() begins the process of creating a new fdt with
+ * the sequential write interface.
+ *
+ * fdt creation process must end with fdt_finished() to produce a valid fdt.
+ *
+ * returns:
+ *	0, on success
+ *	-FDT_ERR_NOSPACE, bufsize is insufficient for a minimal fdt
+ *	-FDT_ERR_BADFLAGS, flags is not valid
+ */
+int fdt_create_with_flags(void *buf, int bufsize, uint32_t flags);
+
+/**
+ * fdt_create - begin creation of a new fdt
+ * @fdt: pointer to memory allocated where fdt will be created
+ * @bufsize: size of the memory space at fdt
+ *
+ * fdt_create() is equivalent to fdt_create_with_flags() with flags=0.
+ *
+ * returns:
+ *	0, on success
+ *	-FDT_ERR_NOSPACE, bufsize is insufficient for a minimal fdt
+ */
 int fdt_create(void *buf, int bufsize);
+
 int fdt_resize(void *fdt, void *buf, int bufsize);
 int fdt_add_reservemap_entry(void *fdt, uint64_t addr, uint64_t size);
 int fdt_finish_reservemap(void *fdt);