sandbox: Add facility to save/restore sandbox state

It is often useful to be able to save out the state from a sandbox test
run, for analysis or to restore it later to continue a test. Add generic
infrastructure for doing this using a device tree binary file. This is
a flexible tagged file format which is already supported by U-Boot, and
it supports hierarchy if needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Hung-ying Tyan <tyanh@chromium.org>

arch/sandbox/include/asm/state.h

@@ -8,6 +8,7 @@
 
 #include <config.h>
 #include <stdbool.h>
+#include <linux/stringify.h>
 
 /* How we exited U-Boot */
 enum exit_type_id {
@@ -34,12 +35,82 @@ struct sandbox_state {
 	unsigned int ram_size;		/* Size of RAM buffer */
 	const char *ram_buf_fname;	/* Filename to use for RAM buffer */
 	bool write_ram_buf;		/* Write RAM buffer on exit */
+	const char *state_fname;	/* File containing sandbox state */
+	void *state_fdt;		/* Holds saved state for sandbox */
+	bool read_state;		/* Read sandbox state on startup */
+	bool write_state;		/* Write sandbox state on exit */
+	bool ignore_missing_state_on_read;	/* No error if state missing */
 
 	/* Pointer to information for each SPI bus/cs */
 	struct sandbox_spi_info spi[CONFIG_SANDBOX_SPI_MAX_BUS]
 					[CONFIG_SANDBOX_SPI_MAX_CS];
 };
 
+/* Minimum space we guarantee in the state FDT when calling read/write*/
+#define SANDBOX_STATE_MIN_SPACE		0x1000
+
+/**
+ * struct sandbox_state_io - methods to saved/restore sandbox state
+ * @name: Name of of the device tree node, also the name of the variable
+ *	holding this data so it should be an identifier (use underscore
+ *	instead of minus)
+ * @compat: Compatible string for the node containing this state
+ *
+ * @read: Function to read state from FDT
+ *	If data is available, then blob and node will provide access to it. If
+ *	not (blob == NULL and node == -1) this function should set up an empty
+ *	data set for start-of-day.
+ *	@param blob: Pointer to device tree blob, or NULL if no data to read
+ *	@param node: Node offset to read from
+ *	@return 0 if OK, -ve on error
+ *
+ * @write: Function to write state to FDT
+ *	The caller will ensure that there is a node ready for the state. The
+ *	node may already contain the old state, in which case it should be
+ *	overridden. There is guaranteed to be SANDBOX_STATE_MIN_SPACE bytes
+ *	of free space, so error checking is not required for fdt_setprop...()
+ *	calls which add up to less than this much space.
+ *
+ *	For adding larger properties, use state_setprop().
+ *
+ * @param blob: Device tree blob holding state
+ * @param node: Node to write our state into
+ *
+ * Note that it is possible to save data as large blobs or as individual
+ * hierarchical properties. However, unless you intend to keep state files
+ * around for a long time and be able to run an old state file on a new
+ * sandbox, it might not be worth using individual properties for everything.
+ * This is certainly supported, it is just a matter of the effort you wish
+ * to put into the state read/write feature.
+ */
+struct sandbox_state_io {
+	const char *name;
+	const char *compat;
+	int (*write)(void *blob, int node);
+	int (*read)(const void *blob, int node);
+};
+
+/**
+ * SANDBOX_STATE_IO - Declare sandbox state to read/write
+ *
+ * Sandbox permits saving state from one run and restoring it in another. This
+ * allows the test system to retain state between runs and thus better
+ * emulate a real system. Examples of state that might be useful to save are
+ * the emulated GPIOs pin settings, flash memory contents and TPM private
+ * data. U-Boot memory contents is dealth with separately since it is large
+ * and it is not normally useful to save it (since a normal system does not
+ * preserve DRAM between runs). See the '-m' option for this.
+ *
+ * See struct sandbox_state_io above for member documentation.
+ */
+#define SANDBOX_STATE_IO(_name, _compat, _read, _write) \
+	ll_entry_declare(struct sandbox_state_io, _name, state_io) = { \
+		.name = __stringify(_name), \
+		.read = _read, \
+		.write = _write, \
+		.compat = _compat, \
+	}
+
 /**
  * Record the exit type to be reported by the test program.
  *
@@ -54,6 +125,49 @@ void state_record_exit(enum exit_type_id exit_type);
  */
 struct sandbox_state *state_get_current(void);
 
+/**
+ * Read the sandbox state from the supplied device tree file
+ *
+ * This calls all registered state handlers to read in the sandbox state
+ * from a previous test run.
+ *
+ * @param state		Sandbox state to update
+ * @param fname		Filename of device tree file to read from
+ * @return 0 if OK, -ve on error
+ */
+int sandbox_read_state(struct sandbox_state *state, const char *fname);
+
+/**
+ * Write the sandbox state to the supplied device tree file
+ *
+ * This calls all registered state handlers to write out the sandbox state
+ * so that it can be preserved for a future test run.
+ *
+ * If the file exists it is overwritten.
+ *
+ * @param state		Sandbox state to update
+ * @param fname		Filename of device tree file to write to
+ * @return 0 if OK, -ve on error
+ */
+int sandbox_write_state(struct sandbox_state *state, const char *fname);
+
+/**
+ * Add a property to a sandbox state node
+ *
+ * This is equivalent to fdt_setprop except that it automatically enlarges
+ * the device tree if necessary. That means it is safe to write any amount
+ * of data here.
+ *
+ * This function can only be called from within struct sandbox_state_io's
+ * ->write method, i.e. within state I/O drivers.
+ *
+ * @param node		Device tree node to write to
+ * @param prop_name	Property to write
+ * @param data		Data to write into property
+ * @param size		Size of data to write into property
+ */
+int state_setprop(int node, const char *prop_name, const void *data, int size);
+
 /**
  * Initialize the test system state
  */