mach-snapdragon: generate fdtfile automatically

With just a few basic rules, we can generate the $fdtfile environment
variable to match the format used in Linux. This uses the root
compatible property inside u-boot, with specific handling for the
Dragonboard845c which is a special case, and for the qrb robotics
boards.

This is known to work on supported platforms, and lets us avoid having a
big lookup table.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Tested-by: Sumit Garg <sumit.garg@linaro.org> #qcs404
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>

arch/arm/mach-snapdragon/board.c

@@ -160,6 +160,106 @@ int board_init(void)
 	return 0;
 }
 
+/* Sets up the "board", and "soc" environment variables as well as constructing the devicetree
+ * path, with a few quirks to handle non-standard dtb filenames. This is not meant to be a
+ * comprehensive solution to automatically picking the DTB, but aims to be correct for the
+ * majority case. For most devices it should be possible to make this algorithm work by
+ * adjusting the root compatible property in the U-Boot DTS. Handling devices with multiple
+ * variants that are all supported by a single U-Boot image will require implementing device-
+ * specific detection.
+ */
+static void configure_env(void)
+{
+	const char *first_compat, *last_compat;
+	char *tmp;
+	char buf[32] = { 0 };
+	/*
+	 * Most DTB filenames follow the scheme: qcom/<soc>-[vendor]-<board>.dtb
+	 * The vendor is skipped when it's a Qualcomm reference board, or the
+	 * db845c.
+	 */
+	char dt_path[64] = { 0 };
+	int compat_count, ret;
+	ofnode root;
+
+	root = ofnode_root();
+	/* This is almost always 2, but be explicit that we want the first and last compatibles
+	 * not the first and second.
+	 */
+	compat_count = ofnode_read_string_count(root, "compatible");
+	if (compat_count < 2) {
+		log_warning("%s: only one root compatible bailing!\n", __func__);
+		return;
+	}
+
+	/* The most specific device compatible (e.g. "thundercomm,db845c") */
+	ret = ofnode_read_string_index(root, "compatible", 0, &first_compat);
+	if (ret < 0) {
+		log_warning("Can't read first compatible\n");
+		return;
+	}
+
+	/* The last compatible is always the SoC compatible */
+	ret = ofnode_read_string_index(root, "compatible", compat_count - 1, &last_compat);
+	if (ret < 0) {
+		log_warning("Can't read second compatible\n");
+		return;
+	}
+
+	/* Copy the second compat (e.g. "qcom,sdm845") into buf */
+	strlcpy(buf, last_compat, sizeof(buf) - 1);
+	tmp = buf;
+
+	/* strsep() is destructive, it replaces the comma with a \0 */
+	if (!strsep(&tmp, ",")) {
+		log_warning("second compatible '%s' has no ','\n", buf);
+		return;
+	}
+
+	/* tmp now points to just the "sdm845" part of the string */
+	env_set("soc", tmp);
+
+	/* Now figure out the "board" part from the first compatible */
+	memset(buf, 0, sizeof(buf));
+	strlcpy(buf, first_compat, sizeof(buf) - 1);
+	tmp = buf;
+
+	/* The Qualcomm reference boards (RBx, HDK, etc)  */
+	if (!strncmp("qcom", buf, strlen("qcom"))) {
+		/*
+		 * They all have the first compatible as "qcom,<soc>-<board>"
+		 * (e.g. "qcom,qrb5165-rb5"). We extract just the part after
+		 * the dash.
+		 */
+		if (!strsep(&tmp, "-")) {
+			log_warning("compatible '%s' has no '-'\n", buf);
+			return;
+		}
+		/* tmp is now "rb5" */
+		env_set("board", tmp);
+	} else {
+		if (!strsep(&tmp, ",")) {
+			log_warning("compatible '%s' has no ','\n", buf);
+			return;
+		}
+		/* for thundercomm we just want the bit after the comma (e.g. "db845c"),
+		 * for all other boards we replace the comma with a '-' and take both
+		 * (e.g. "oneplus-enchilada")
+		 */
+		if (!strncmp("thundercomm", buf, strlen("thundercomm"))) {
+			env_set("board", tmp);
+		} else {
+			*(tmp - 1) = '-';
+			env_set("board", buf);
+		}
+	}
+
+	/* Now build the full path name */
+	snprintf(dt_path, sizeof(dt_path), "qcom/%s-%s.dtb",
+		 env_get("soc"), env_get("board"));
+	env_set("fdtfile", dt_path);
+}
+
 void __weak qcom_late_init(void)
 {
 }
@@ -188,6 +288,7 @@ int board_late_init(void)
 	if (status)
 		log_warning("%s: Failed to set run time variables\n", __func__);
 
+	configure_env();
 	qcom_late_init();
 
 	return 0;