ns16550: command line parsing adjustments

Allow intermediate parts of the command line options to be absent
(expressed by two immediately succeeding commas).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

docs/misc/xen-command-line.markdown

@@ -199,7 +199,7 @@ If set, override Xen's calculation of the level 2 cache line size.
 If set, override Xen's default choice for the platform timer.
 
 ### com1,com2
-> `= <baud>[/<clock_hz>][,DPS[,<io-base>[,<irq>[,<port-bdf>[,<bridge-bdf>]]]] | pci | amt ] `
+> `= <baud>[/<clock_hz>][,[DPS][,[<io-base>|pci|amt][,[<irq>][,[<port-bdf>][,[<bridge-bdf>]]]]]]`
 
 Both option `com1` and `com2` follow the same format.
 

xen/drivers/char/ns16550.c

@@ -555,26 +555,23 @@ static void __init ns16550_parse_port_config(
     else if ( (baud = simple_strtoul(conf, &conf, 10)) != 0 )
         uart->baud = baud;
 
-    if ( *conf == '/')
+    if ( *conf == '/' )
     {
         conf++;
         uart->clock_hz = simple_strtoul(conf, &conf, 0) << 4;
     }
 
-    if ( *conf != ',' )
-        goto config_parsed;
-    conf++;
-
-    uart->data_bits = simple_strtoul(conf, &conf, 10);
-
-    uart->parity = parse_parity_char(*conf);
-    conf++;
-
-    uart->stop_bits = simple_strtoul(conf, &conf, 10);
-
-    if ( *conf == ',' )
+    if ( *conf == ',' && *++conf != ',' )
+    {
+        uart->data_bits = simple_strtoul(conf, &conf, 10);
+
+        uart->parity = parse_parity_char(*conf);
+
+        uart->stop_bits = simple_strtoul(conf + 1, &conf, 10);
+    }
+
+    if ( *conf == ',' && *++conf != ',' )
     {
-        conf++;
         if ( strncmp(conf, "pci", 3) == 0 )
         {
             if ( pci_uart_config(uart, 1/* skip AMT */, uart - ns16550_com) )
@@ -591,24 +588,21 @@ static void __init ns16550_parse_port_config(
         {
             uart->io_base = simple_strtoul(conf, &conf, 0);
         }
+    }
 
-        if ( *conf == ',' )
-        {
-            conf++;
-            uart->irq = simple_strtoul(conf, &conf, 10);
-            if ( *conf == ',' )
-            {
-                conf++;
-                uart->ps_bdf_enable = 1;
-                parse_pci_bdf(&conf, &uart->ps_bdf[0]);
-                if ( *conf == ',' )
-                {
-                    conf++;
-                    uart->pb_bdf_enable = 1;
-                    parse_pci_bdf(&conf, &uart->pb_bdf[0]);
-                }
-            }
-        }
+    if ( *conf == ',' && *++conf != ',' )
+        uart->irq = simple_strtol(conf, &conf, 10);
+
+    if ( *conf == ',' && *++conf != ',' )
+    {
+        uart->ps_bdf_enable = 1;
+        parse_pci_bdf(&conf, &uart->ps_bdf[0]);
+    }
+
+    if ( *conf == ',' && *++conf != ',' )
+    {
+        uart->pb_bdf_enable = 1;
+        parse_pci_bdf(&conf, &uart->pb_bdf[0]);
     }
 
  config_parsed: