mbim: Parse MBIM descriptors

This is needed to find out the maximum fragment size that this device
supports.  The minimum length specified in the spec is 64, however 512
bytes is recommended.

We also attempt to parse how many simultaneous commands can be
outstanding at a given time.  In theory MBIM supports multiple
outstanding commands through the use of transaction-id matching, but it
seems some devices only support a single outstanding command at a time.

plugins/mbim.c

@@ -26,6 +26,10 @@
 #define _GNU_SOURCE
 #include <errno.h>
 #include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <linux/types.h>
 #include <unistd.h>
 #include <stdlib.h>
 
@@ -36,19 +40,66 @@
 
 #include <ell/ell.h>
 
+#include <drivers/mbimmodem/mbim-desc.h>
 #include <drivers/mbimmodem/util.h>
 
 struct mbim_data {
 	struct mbim_device *device;
+	uint16_t max_segment;
+	uint8_t max_outstanding;
 };
 
+static int mbim_parse_descriptors(struct mbim_data *md, const char *file)
+{
+	void *data;
+	size_t len;
+	const struct mbim_desc *desc = NULL;
+	const struct mbim_extended_desc *ext_desc = NULL;
+
+	data = l_file_get_contents(file, &len);
+	if (!data)
+		return -EIO;
+
+	if (!mbim_find_descriptors(data, len, &desc, &ext_desc)) {
+		l_free(data);
+		return -ENOENT;
+	}
+
+	if (desc)
+		md->max_segment = L_LE16_TO_CPU(desc->wMaxControlMessage);
+
+	if (ext_desc)
+		md->max_outstanding = ext_desc->bMaxOutstandingCommandMessages;
+
+	l_free(data);
+	return 0;
+}
+
 static int mbim_probe(struct ofono_modem *modem)
 {
+	const char *descriptors;
 	struct mbim_data *data;
+	int err;
 
 	DBG("%p", modem);
 
+	descriptors = ofono_modem_get_string(modem, "DescriptorFile");
+
+	if (!descriptors)
+		return -EINVAL;
+
 	data = l_new(struct mbim_data, 1);
+	data->max_outstanding = 1;
+
+	err = mbim_parse_descriptors(data, descriptors);
+	if (err < 0) {
+		DBG("Warning, unable to load descriptors, setting defaults");
+		data->max_segment = 512;
+	}
+
+	DBG("MaxSegment: %d, MaxOutstanding: %d",
+			data->max_segment, data->max_outstanding);
+
 	ofono_modem_set_data(modem, data);
 
 	return 0;