[PATCH v3 1/2] term/serial: Add support for PCI serial devices

[Glenn Washburn]

From: "peterz@infradead.org" <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"

Documentation is added to note that serial devices found on the PCI bus will
be exposed as "pci,XX:XX.X" and how to find serial terminal logical names.
Also, some minor documentation improvements were added.

This can be tested in QEMU by adding a pci-serial device, eg. using the option
"-device pci-serial".

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Glenn Washburn <development@efficientek.com>
Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 docs/grub.texi              | 13 ++++--
 grub-core/Makefile.core.def |  1 +
 grub-core/term/pci/serial.c | 91 +++++++++++++++++++++++++++++++++++++
 grub-core/term/serial.c     |  6 ++-
 include/grub/pci.h          |  5 ++
 include/grub/serial.h       |  4 ++
 6 files changed, 116 insertions(+), 4 deletions(-)
 create mode 100644 grub-core/term/pci/serial.c

diff --git a/docs/grub.texi b/docs/grub.texi
index a3e9ce2d1ac7..477919ee901b 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -2716,8 +2716,7 @@ grub> @kbd{terminal_input serial; terminal_output serial}
 The command @command{serial} initializes the serial unit 0 with the
 speed 9600bps. The serial unit 0 is usually called @samp{COM1}, so, if
 you want to use COM2, you must specify @samp{--unit=1} instead. This
-command accepts many other options, so please refer to @ref{serial},
-for more details.
+command accepts many other options, @pxref{serial} for more details.
 
 Without argument or with @samp{--port=auto}, GRUB will attempt to use
 ACPI when available to auto-detect the default serial port and its
@@ -4186,6 +4185,9 @@ Additionally, an MMIO address can be suffixed with:
 @samp{.q} for 64-bit long long word access
 @end itemize
 
+Also, @var{port} can be of the form @samp{pci,XX:XX.X} to indicate a serial
+device exposed on the PCI bus.
+
 @var{speed} is the transmission speed; default is 9600. @var{word} and
 @var{stop} are the number of data bits and stop bits. Data bits must
 be in the range 5-8 and stop bits must be 1 or 2. Default is 8 data
@@ -4201,10 +4203,15 @@ The serial port is not used as a communication channel 
unless the
 @command{terminal_input} or @command{terminal_output} command is used
 (@pxref{terminal_input}, @pxref{terminal_output}).
 
+Note, valid @var{port} values, excluding IO port addresses, can be found
+by listing terminals with @command{terminal_output}, selecting all names
+prefixed by @samp{serial_} and removing that prefix.
+
 Examples:
 @example
-serial --port=3f8 --speed=9600
+serial --port=0x3f8 --speed=9600
 serial --port=mmio,fefb0000.l --speed=115200
+serial --port=pci,00:16.3 --speed=115200
 @end example
 
 See also @ref{Serial terminal}.
diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 801df7c21de6..fb4cc066c526 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -2064,6 +2064,7 @@ module = {
   ieee1275 = term/ieee1275/serial.c;
   mips_arc = term/arc/serial.c;
   efi = term/efi/serial.c;
+  x86 = term/pci/serial.c;
 
   enable = terminfomodule;
   enable = ieee1275;
diff --git a/grub-core/term/pci/serial.c b/grub-core/term/pci/serial.c
new file mode 100644
index 000000000000..0b8fe815f5ca
--- /dev/null
+++ b/grub-core/term/pci/serial.c
@@ -0,0 +1,91 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2023  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 __attribute__ 
((unused)), void *data __attribute__ ((unused)))
+{
+  grub_pci_address_t cmd_addr, class_addr, bar_addr;
+  struct grub_serial_port *port;
+  grub_uint32_t class, bar;
+  grub_uint16_t cmdreg;
+  grub_err_t err;
+
+  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,%02x:%02x.%x",
+                              grub_pci_get_bus (dev),
+                              grub_pci_get_device (dev),
+                              grub_pci_get_function (dev));
+  if (port->name == NULL)
+    goto fail;
+
+  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 fail;
+    }
+
+  err = grub_serial_register (port);
+  if (err != GRUB_ERR_NONE)
+    goto fail;
+
+  return 0;
+
+ fail:
+  grub_free (port->name);
+  grub_free (port);
+  return 0;
+}
+
+void
+grub_pciserial_init (void)
+{
+  grub_pci_iterate (find_pciserial, NULL);
+}
diff --git a/grub-core/term/serial.c b/grub-core/term/serial.c
index c65ffc63cecb..05db4cf177c2 100644
--- a/grub-core/term/serial.c
+++ b/grub-core/term/serial.c
@@ -255,7 +255,8 @@ grub_cmd_serial (grub_extcmd_context_t ctxt, int argc, char 
**args)
 
   if (state[OPTION_PORT].set)
     {
-      if (grub_strncmp (state[OPTION_PORT].arg, "mmio,", sizeof ("mmio,") - 1) 
== 0)
+      if (grub_strncmp (state[OPTION_PORT].arg, "mmio,", sizeof ("mmio,") - 1) 
== 0 ||
+         grub_strncmp (state[OPTION_PORT].arg, "pci,", sizeof ("pci,") - 1) == 
0)
           grub_snprintf (pname, sizeof (pname), "%s", state[1].arg);
       else
           grub_snprintf (pname, sizeof (pname), "port%lx",
@@ -505,6 +506,9 @@ GRUB_MOD_INIT(serial)
 #ifdef GRUB_MACHINE_ARC
   grub_arcserial_init ();
 #endif
+#ifdef GRUB_HAS_PCI
+  grub_pciserial_init ();
+#endif
 }
 
 GRUB_MOD_FINI(serial)
diff --git a/include/grub/pci.h b/include/grub/pci.h
index 262c89b748bb..b228bb1b71fd 100644
--- a/include/grub/pci.h
+++ b/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
 
diff --git a/include/grub/serial.h b/include/grub/serial.h
index a955c076d892..9226d51f5831 100644
--- a/include/grub/serial.h
+++ b/include/grub/serial.h
@@ -210,6 +210,10 @@ grub_arcserial_init (void);
 struct grub_serial_port *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);
-- 
2.34.1