PXE: FDT: Add support for fdt in PXE

Now DT support is becoming common for all new SoC's. Hence it is better
to have option for getting specific FDT from the remote server.

This patch adds support for new label i.e. 'fdt'. This will allow to
retrieve 'fdt blob' from the remote server. This patch take care for
the following scenarios.

The usage of fdt is optional.
The 'fdt blob' can be retrieved from tftp or can be available locally
or can be absent.

If 'fdt_addr_r' environment variable is set and 'fdt' label is defined
retrieve 'fdt blob' from tftp. 'fdt_addr_r' is then passed along bootm
command.

If 'fdt_addr' is set and 'fdt blob' is not retrieved from the tftp pass
'fdt_addr' to bootm command. In this case 'fdt blob' will be available
at 'fdt_addr'.

If 'fdt_addr' is not set and 'fdt blob' is not retrieve from tftp pass
NULL to boot command. In this case 'fdt blob' is not required and absent.

Signed-off-by: Chander Kashyap <chander.kashyap@linaro.org>
Acked-by: Jason Hobbs <jason.hobbs@calxeda.com>

common/cmd_pxe.c

@@ -450,6 +450,7 @@ struct pxe_label {
 	char *kernel;
 	char *append;
 	char *initrd;
+	char *fdt;
 	int attempted;
 	int localboot;
 	struct list_head list;
@@ -517,6 +518,9 @@ static void label_destroy(struct pxe_label *label)
 	if (label->initrd)
 		free(label->initrd);
 
+	if (label->fdt)
+		free(label->fdt);
+
 	free(label);
 }
 
@@ -541,6 +545,9 @@ static void label_print(void *data)
 
 	if (label->initrd)
 		printf("\t\tinitrd: %s\n", label->initrd);
+
+	if (label->fdt)
+		printf("\tfdt: %s\n", label->fdt);
 }
 
 /*
@@ -628,10 +635,29 @@ static void label_boot(struct pxe_label *label)
 	bootm_argv[1] = getenv("kernel_addr_r");
 
 	/*
-	 * fdt usage is optional.  If there is an fdt_addr specified, we will
-	 * pass it along to bootm, and adjust argc appropriately.
+	 * fdt usage is optional:
+	 * It handles the following scenarios. All scenarios are exclusive
+	 *
+	 * Scenario 1: If fdt_addr_r specified and "fdt" label is defined in
+	 * pxe file, retrieve fdt blob from server. Pass fdt_addr_r to bootm,
+	 * and adjust argc appropriately.
+	 *
+	 * Scenario 2: If there is an fdt_addr specified, pass it along to
+	 * bootm, and adjust argc appropriately.
+	 *
+	 * Scenario 3: fdt blob is not available.
 	 */
-	bootm_argv[3] = getenv("fdt_addr");
+	bootm_argv[3] = getenv("fdt_addr_r");
+
+	/* if fdt label is defined then get fdt from server */
+	if (bootm_argv[3] && label->fdt) {
+		if (get_relfile_envaddr(label->fdt, "fdt_addr_r") < 0) {
+			printf("Skipping %s for failure retrieving fdt\n",
+					label->name);
+			return;
+		}
+	} else
+		bootm_argv[3] = getenv("fdt_addr");
 
 	if (bootm_argv[3])
 		bootm_argc = 4;
@@ -658,6 +684,7 @@ enum token_type {
 	T_DEFAULT,
 	T_PROMPT,
 	T_INCLUDE,
+	T_FDT,
 	T_INVALID
 };
 
@@ -685,6 +712,7 @@ static const struct token keywords[] = {
 	{"append", T_APPEND},
 	{"initrd", T_INITRD},
 	{"include", T_INCLUDE},
+	{"fdt", T_FDT},
 	{NULL, T_INVALID}
 };
 
@@ -1074,6 +1102,11 @@ static int parse_label(char **c, struct pxe_menu *cfg)
 				err = parse_sliteral(c, &label->initrd);
 			break;
 
+		case T_FDT:
+			if (!label->fdt)
+				err = parse_sliteral(c, &label->fdt);
+			break;
+
 		case T_LOCALBOOT:
 			err = parse_integer(c, &label->localboot);
 			break;

doc/README.pxe

@@ -93,8 +93,13 @@ pxe boot
      be passed to the bootm command to boot the kernel. These environment
      variables are required to be set.
 
-     fdt_addr - the location of a fdt blob. If this is set, it will be passed
-     to bootm when booting a kernel.
+     fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it
+     retrieves from tftp. The retrieval is possible if 'fdt' label is defined in
+     pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r'
+     will be passed to bootm command to boot the kernel.
+
+     fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm
+     command if it is set and 'fdt_addr_r' is not passed to bootm command.
 
 pxe file format
 ===============
@@ -156,6 +161,11 @@ initrd <path>	    - if this label is chosen, use tftp to retrieve the initrd
 		      the initrd_addr_r environment variable, and that address
 		      will be passed to bootm.
 
+fdt <path>	    - if this label is chosen, use tftp to retrieve the fdt blob
+		      at <path>. it will be stored at the address indicated in
+		      the fdt_addr_r environment variable, and that address will
+		      be passed to bootm.
+
 localboot <flag>    - Run the command defined by "localcmd" in the environment.
 		      <flag> is ignored and is only here to match the syntax of
 		      PXELINUX config files.