drivers/char: add support for selecting specific xhci

Handle parameters similar to dbgp=ehci.

Implement this by not resettting dbc->sbdf again in dbc_init_xhc(), but
using a value found there if non-zero. Additionally, add xue->xhc_num to
select n-th controller.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

docs/misc/xen-command-line.pandoc

@@ -721,7 +721,7 @@ Available alternatives, with their meaning, are:
 
 ### dbgp
 > `= ehci[ <integer> | @pci<bus>:<slot>.<func> ]`
-> `= xhci`
+> `= xhci[ <integer> | @pci<bus>:<slot>.<func> ]`
 
 Specify the USB controller to use, either by instance number (when going
 over the PCI busses sequentially) or by PCI device (must be on segment 0).

xen/drivers/char/xhci-dbc.c

@@ -246,6 +246,7 @@ struct dbc {
     void __iomem *xhc_mmio;
 
     bool open;
+    unsigned int xhc_num; /* look for n-th xhc */
 };
 
 static void *dbc_sys_map_xhc(uint64_t phys, size_t size)
@@ -278,9 +279,11 @@ static bool __init dbc_init_xhc(struct dbc *dbc)
     uint16_t cmd;
     size_t xhc_mmio_size;
 
+    if ( dbc->sbdf.sbdf == 0 )
+    {
         /*
-     * Search PCI bus 0 for the xHC. All the host controllers supported so far
-     * are part of the chipset and are on bus 0.
+         * Search PCI bus 0 for the xHC. All the host controllers supported so
+         * far are part of the chipset and are on bus 0.
          */
         for ( devfn = 0; devfn < 256; devfn++ )
         {
@@ -289,13 +292,24 @@ static bool __init dbc_init_xhc(struct dbc *dbc)
 
             if ( hdr == 0 || hdr == 0x80 )
             {
-            if ( (pci_conf_read32(sbdf, PCI_CLASS_REVISION) >> 8) == DBC_XHC_CLASSC )
+                if ( (pci_conf_read32(sbdf, PCI_CLASS_REVISION) >> 8) ==
+                     DBC_XHC_CLASSC )
                 {
+                    if ( dbc->xhc_num-- )
+                        continue;
                     dbc->sbdf = sbdf;
                     break;
                 }
             }
         }
+    }
+    else
+    {
+        /* Verify if selected device is really xHC */
+        if ( (pci_conf_read32(dbc->sbdf, PCI_CLASS_REVISION) >> 8) !=
+             DBC_XHC_CLASSC )
+            dbc->sbdf.sbdf = 0;
+    }
 
     if ( !dbc->sbdf.sbdf )
     {
@@ -1052,12 +1066,33 @@ void __init xhci_dbc_uart_init(void)
 {
     struct dbc_uart *uart = &dbc_uart;
     struct dbc *dbc = &uart->dbc;
+    const char *e;
 
     if ( strncmp(opt_dbgp, "xhci", 4) )
         return;
 
     memset(dbc, 0, sizeof(*dbc));
 
+    if ( isdigit(opt_dbgp[4]) )
+    {
+        dbc->xhc_num = simple_strtoul(opt_dbgp + 4, &e, 10);
+    }
+    else if ( strncmp(opt_dbgp + 4, "@pci", 4) == 0 )
+    {
+        unsigned int bus, slot, func;
+
+        e = parse_pci(opt_dbgp + 8, NULL, &bus, &slot, &func);
+        if ( !e || *e )
+        {
+            printk(XENLOG_ERR
+                   "Invalid dbgp= PCI device spec: '%s'\n",
+                   opt_dbgp + 8);
+            return;
+        }
+
+        dbc->sbdf = PCI_SBDF(0, bus, slot, func);
+    }
+
     dbc->dbc_ctx = &ctx;
     dbc->dbc_erst = &erst;
     dbc->dbc_ering.trb = evt_trb;