[PATCH] term/serial: Add support for PCI serial devices

[Peter Zijlstra <peterz@infradead.org>]

Loosely based on early_pci_serial_init() from Linux, allow GRUB to make
use of PCI serial devices.

Specifically, my Alderlake NUC exposes the Intel AMT SoL UART as a PCI
enumerated device but doesn't include it in the EFI tables.

Tested and confirmed working on a "Lenovo P360 Tiny" with Intel AMT
enabled. This specific machine has (from lspci -vv):

00:16.3 Serial controller: Intel Corporation Device 7aeb (rev 11) (prog-if 02 [16550])
        DeviceName: Onboard - Other
        Subsystem: Lenovo Device 330e
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Interrupt: pin D routed to IRQ 19
        Region 0: I/O ports at 40a0 [size=8]
        Region 1: Memory at b4224000 (32-bit, non-prefetchable) [size=4K]
        Capabilities: [40] MSI: Enable- Count=1/1 Maskable- 64bit+
                Address: 0000000000000000  Data: 0000
        Capabilities: [50] Power Management version 3
                Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
                Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
        Kernel driver in use: serial

From which the following config (/etc/default/grub) gets a working
serial setup:

GRUB_CMDLINE_LINUX="console=tty0 earlyprintk=pciserial,00:16.3,115200 console=ttyS0,115200"
GRUB_SERIAL_COMMAND="serial --port=0x40a0 --speed=115200"
GRUB_TERMINAL="serial console"

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 grub-core/term/serial.c |   59 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/grub/pci.h      |    3 ++
 include/grub/serial.h   |    2 +
 3 files changed, 64 insertions(+)

Index: grub2-2.06/grub-core/term/serial.c
===================================================================
--- grub2-2.06.orig/grub-core/term/serial.c
+++ grub2-2.06/grub-core/term/serial.c
@@ -34,6 +34,7 @@
 #ifdef GRUB_MACHINE_IEEE1275
 #include <grub/ieee1275/console.h>
 #endif
+#include <grub/pci.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -448,6 +449,7 @@ GRUB_MOD_INIT(serial)
 #ifdef GRUB_MACHINE_ARC
   grub_arcserial_init ();
 #endif
+  grub_pciserial_init ();
 }
 
 GRUB_MOD_FINI(serial)
@@ -461,3 +463,60 @@ GRUB_MOD_FINI(serial)
     }
   grub_unregister_extcmd (cmd);
 }
+
+#define GRUB_SERIAL_PORT_NUM 4
+static char com_names[GRUB_SERIAL_PORT_NUM][20];
+static struct grub_serial_port com_ports[GRUB_SERIAL_PORT_NUM];
+static int ports = 0;
+
+static int
+find_pciserial (grub_pci_device_t dev, grub_pci_id_t pciid, void *data)
+{
+  grub_pci_address_t cmd_addr, class_addr, bar_addr;
+  grub_uint32_t class, bar;
+  grub_uint16_t cmdreg;
+  int err, i = ports;
+
+  (void)data;
+  (void)pciid;
+
+  cmd_addr = grub_pci_make_address (dev, GRUB_PCI_REG_COMMAND);
+  cmdreg = grub_pci_read (cmd_addr);
+
+  class_addr = grub_pci_make_address (dev, GRUB_PCI_REG_REVISION);
+  class = grub_pci_read (class_addr);
+
+  bar_addr = grub_pci_make_address (dev, GRUB_PCI_REG_ADDRESS_REG0);
+  bar = grub_pci_read (bar_addr);
+
+  /* MODEM, SERIAL or MAGIC */
+  if (((class >> 16) != GRUB_PCI_CLASS_COMMUNICATION_MODEM &&
+       (class >> 16) != GRUB_PCI_CLASS_COMMUNICATION_SERIAL) ||
+      ((class >> 8) & 0xff) != 0x02)
+	  return 0;
+
+  if (!(bar & 1)) /* Not I/O */
+	  return 0;
+
+  grub_pci_write (cmd_addr, cmdreg | GRUB_PCI_COMMAND_IO_ENABLED);
+
+  grub_snprintf (com_names[i], sizeof (com_names[i]), "pci%d", i);
+  com_ports[i].name = com_names[i];
+  com_ports[i].driver = &grub_ns8250_driver;
+  com_ports[i].port = bar & 0xfffffffc;
+  err = grub_serial_config_defaults (&com_ports[i]);
+  if (err) {
+	  grub_print_error();
+	  return 0;
+  }
+
+  grub_serial_register (&com_ports[i]);
+
+  return ++ports >= GRUB_SERIAL_PORT_NUM;
+}
+
+void
+grub_pciserial_init (void)
+{
+	grub_pci_iterate (find_pciserial, NULL);
+}
Index: grub2-2.06/include/grub/serial.h
===================================================================
--- grub2-2.06.orig/include/grub/serial.h
+++ grub2-2.06/include/grub/serial.h
@@ -193,6 +193,8 @@ const char *
 grub_arcserial_add_port (const char *path);
 #endif
 
+void grub_pciserial_init (void);
+
 struct grub_serial_port *grub_serial_find (const char *name);
 extern struct grub_serial_driver grub_ns8250_driver;
 void EXPORT_FUNC(grub_serial_unregister_driver) (struct grub_serial_driver *driver);
Index: grub2-2.06/include/grub/pci.h
===================================================================
--- grub2-2.06.orig/include/grub/pci.h
+++ grub2-2.06/include/grub/pci.h
@@ -83,6 +83,9 @@
 #define  GRUB_PCI_CLASS_SUBCLASS_VGA  0x0300
 #define  GRUB_PCI_CLASS_SUBCLASS_USB  0x0c03
 
+#define  GRUB_PCI_CLASS_COMMUNICATION_SERIAL  0x0700
+#define  GRUB_PCI_CLASS_COMMUNICATION_MODEM   0x0703
+
 #ifndef ASM_FILE
 
 enum