[PATCH v2 2/3] term/serial: Add support for PCI serial devices

[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>
---

Index: grub/grub-core/Makefile.core.def
===================================================================
--- grub.orig/grub-core/Makefile.core.def
+++ grub/grub-core/Makefile.core.def
@@ -2047,6 +2047,7 @@ module = {
   ieee1275 = term/ieee1275/serial.c;
   mips_arc = term/arc/serial.c;
   efi = term/efi/serial.c;
+  pci = term/pci/serial.c;
 
   enable = terminfomodule;
   enable = ieee1275;
Index: grub/grub-core/term/pci/serial.c
===================================================================
--- /dev/null
+++ grub/grub-core/term/pci/serial.c
@@ -0,0 +1,95 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2022  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/serial.h>
+#include <grub/term.h>
+#include <grub/types.h>
+#include <grub/pci.h>
+#include <grub/mm.h>
+#include <grub/misc.h>
+
+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;
+  struct grub_serial_port *port;
+  grub_uint32_t class, bar;
+  grub_uint16_t cmdreg;
+  int *port_num = data;
+  grub_err_t err;
+
+  (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);
+
+  /* 16550 compattible MODEM or SERIAL */
+  if (((class >> 16) != GRUB_PCI_CLASS_COMMUNICATION_MODEM &&
+       (class >> 16) != GRUB_PCI_CLASS_COMMUNICATION_SERIAL) ||
+      ((class >> 8) & 0xff) != GRUB_PCI_SERIAL_16550_COMPATIBLE)
+    return 0;
+
+  if ((bar & GRUB_PCI_ADDR_SPACE_MASK) != GRUB_PCI_ADDR_SPACE_IO)
+    return 0;
+
+  port = grub_zalloc (sizeof (*port));
+  if (port == NULL)
+    return 0;
+
+  port->name = grub_xasprintf ("pci%d", (*port_num));
+  if (port->name == NULL)
+    goto error;
+
+  grub_pci_write (cmd_addr, cmdreg | GRUB_PCI_COMMAND_IO_ENABLED);
+
+  port->driver = &grub_ns8250_driver;
+  port->port = bar & GRUB_PCI_ADDR_IO_MASK;
+  err = grub_serial_config_defaults (port);
+  if (err != GRUB_ERR_NONE)
+    {
+      grub_print_error ();
+      goto error;
+    }
+
+  err = grub_serial_register (port);
+  if (err != GRUB_ERR_NONE)
+    goto error;
+
+  (*port_num)++;
+
+  return 0;
+
+error:
+  grub_free (port->name);
+  grub_free (port);
+  return 0;
+}
+
+void
+grub_pciserial_init (void)
+{
+  int port_num;
+
+  grub_pci_iterate (find_pciserial, &port_num);
+}
Index: grub/grub-core/term/serial.c
===================================================================
--- grub.orig/grub-core/term/serial.c
+++ grub/grub-core/term/serial.c
@@ -448,6 +448,9 @@ GRUB_MOD_INIT(serial)
 #ifdef GRUB_MACHINE_ARC
   grub_arcserial_init ();
 #endif
+#ifdef GRUB_HAS_PCI
+  grub_pciserial_init ();
+#endif
 }
 
 GRUB_MOD_FINI(serial)
Index: grub/include/grub/pci.h
===================================================================
--- grub.orig/include/grub/pci.h
+++ grub/include/grub/pci.h
@@ -80,8 +80,13 @@
 
 #define  GRUB_PCI_STATUS_DEVSEL_TIMING_SHIFT 9
 #define  GRUB_PCI_STATUS_DEVSEL_TIMING_MASK 0x0600
+
 #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
+
+#define  GRUB_PCI_SERIAL_16550_COMPATIBLE 0x02
 
 #ifndef ASM_FILE
 
Index: grub/include/grub/serial.h
===================================================================
--- grub.orig/include/grub/serial.h
+++ grub/include/grub/serial.h
@@ -193,6 +193,10 @@ const char *
 grub_arcserial_add_port (const char *path);
 #endif
 
+#ifdef GRUB_HAS_PCI
+void grub_pciserial_init (void);
+#endif
+
 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);