[PATCH QEMU v2 3/5] Add a GPIO backend using libgpiod

[Geert Uytterhoeven]

Add a GPIO controller backend, to connect virtual GPIOs on the guest to
physical GPIOs on the host.  This allows the guest to control any
external device connected to the physical GPIOs.

Features and limitations:
  - The backend uses libgpiod on Linux,
  - For now only GPIO outputs are supported,
  - The number of GPIO lines mapped is limited to the number of GPIO
    lines available on the virtual GPIO controller.

Future work:
  - GPIO inputs,
  - GPIO line configuration,
  - Optimizations for controlling multiple GPIO lines at once,
  - ...

Signed-off-by: Geert Uytterhoeven <address@hidden>
---
v2:
  - Drop vgpios and gpios parameters, and map the full gpiochip instead,
  - Replace hardcoded PL061 instance by multiple dynamic instances,
    registered through qemu_gpiodev_add().
---
 MAINTAINERS              |  6 +++
 backends/Makefile.objs   |  2 +
 backends/gpiodev.c       | 94 ++++++++++++++++++++++++++++++++++++++++
 configure                | 28 ++++++++++++
 include/sysemu/gpiodev.h | 12 +++++
 5 files changed, 142 insertions(+)
 create mode 100644 backends/gpiodev.c
 create mode 100644 include/sysemu/gpiodev.h

diff --git a/MAINTAINERS b/MAINTAINERS
index e760f65270d29d5d..a70af47430083d14 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -607,6 +607,12 @@ F: include/hw/arm/digic.h
 F: hw/*/digic*
 F: include/hw/*/digic*
 
+GPIO device backend
+M: Geert Uytterhoeven <address@hidden>
+S: Supported
+F: backends/gpiodev.c
+F: include/sysemu/gpiodev.h
+
 Goldfish RTC
 M: Anup Patel <address@hidden>
 M: Alistair Francis <address@hidden>
diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index 28a847cd571d96ed..ee658e797454119a 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -21,3 +21,5 @@ common-obj-$(CONFIG_LINUX) += hostmem-memfd.o
 common-obj-$(CONFIG_GIO) += dbus-vmstate.o
 dbus-vmstate.o-cflags = $(GIO_CFLAGS)
 dbus-vmstate.o-libs = $(GIO_LIBS)
+
+common-obj-$(CONFIG_GPIODEV) += gpiodev.o
diff --git a/backends/gpiodev.c b/backends/gpiodev.c
new file mode 100644
index 0000000000000000..df1bd0113c7b2985
--- /dev/null
+++ b/backends/gpiodev.c
@@ -0,0 +1,94 @@
+/*
+ * QEMU GPIO Backend
+ *
+ * Copyright (C) 2018-2020 Glider bv
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <errno.h>
+#include <gpiod.h>
+
+#include "qemu/osdep.h"
+#include "qemu/config-file.h"
+#include "qemu/cutils.h"
+#include "qemu/error-report.h"
+#include "qemu/module.h"
+#include "qemu/option.h"
+#include "qapi/error.h"
+
+#include "sysemu/gpiodev.h"
+
+#include "hw/irq.h"
+#include "hw/qdev-core.h"
+
+static void gpiodev_irq_handler(void *opaque, int n, int level)
+{
+    struct gpiod_line *line = opaque;
+    int status;
+
+    status = gpiod_line_set_value(line, level);
+    if (status < 0) {
+        struct gpiod_chip *chip = gpiod_line_get_chip(line);
+
+        error_report("%s/%s: Cannot set GPIO line %u: %s",
+                     gpiod_chip_name(chip), gpiod_chip_label(chip),
+                     gpiod_line_offset(line), strerror(errno));
+    }
+}
+
+static int gpiodev_map_line(DeviceState *dev, struct gpiod_chip *chip,
+                            unsigned int gpio, Error **errp)
+{
+    struct gpiod_line *line;
+    qemu_irq irq;
+    int status;
+
+    line = gpiod_chip_get_line(chip, gpio);
+    if (!line) {
+        error_setg(errp, "Cannot obtain GPIO line %u: %s", gpio,
+                   strerror(errno));
+        return -1;
+    }
+
+    status = gpiod_line_request_output(line, "qemu", 0);
+    if (status < 0) {
+        error_setg(errp, "Cannot request GPIO line %u for output: %s", gpio,
+                   strerror(errno));
+        return status;
+    }
+
+    irq = qemu_allocate_irq(gpiodev_irq_handler, line, 0);
+    qdev_connect_gpio_out(dev, gpio, irq);
+    return 0;
+}
+
+void qemu_gpiodev_add(DeviceState *dev, const char *name, unsigned int maxgpio,
+                      Error **errp)
+{
+    struct gpiod_chip *chip;
+    unsigned int i, n;
+    int status;
+
+    chip = gpiod_chip_open_lookup(name);
+    if (!chip) {
+        error_setg(errp, "Cannot open GPIO chip %s: %s", name,
+                   strerror(errno));
+        return;
+    }
+
+    n = gpiod_chip_num_lines(chip);
+    if (n > maxgpio) {
+        warn_report("Last %u GPIO line(s) will not be mapped", n - maxgpio);
+        n = maxgpio;
+    }
+
+    for (i = 0; i < n; i++) {
+        status = gpiodev_map_line(dev, chip, i, errp);
+        if (status < 0) {
+            return;
+        }
+    }
+
+    info_report("Mapped %u GPIO lines", n);
+}
diff --git a/configure b/configure
index 23b5e93752b6a259..8b133402ef727c8e 100755
--- a/configure
+++ b/configure
@@ -509,6 +509,7 @@ libpmem=""
 default_devices="yes"
 plugins="no"
 fuzzing="no"
+gpio=""
 
 supported_cpu="no"
 supported_os="no"
@@ -1601,6 +1602,10 @@ for opt do
   ;;
   --gdb=*) gdb_bin="$optarg"
   ;;
+  --disable-gpio) gpio="no"
+  ;;
+  --enable-gpio) gpio="yes"
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1894,6 +1899,7 @@ disabled with --disable-FEATURE, default is enabled if 
available:
   debug-mutex     mutex debugging support
   libpmem         libpmem support
   xkbcommon       xkbcommon support
+  gpio            gpio support
 
 NOTE: The object files are built at the place where configure is launched
 EOF
@@ -6250,6 +6256,23 @@ case "$slirp" in
     ;;
 esac
 
+##########################################
+# check for libgpiod
+
+if test "$gpio" != "no"; then
+    if $pkg_config --exists "libgpiod"; then
+        gpio="yes"
+        libgpiod_libs=$($pkg_config --libs libgpiod)
+        libgpiod_cflags=$($pkg_config --cflags libgpiod)
+        libs_softmmu="$libs_softmmu $libgpiod_libs"
+        QEMU_CFLAGS="$QEMU_CFLAGS $libgpiod_cflags"
+    else
+        if test "$gpio" = "yes" ; then
+            feature_not_found "gpio" "Install libgpiod"
+        fi
+        gpio="no"
+    fi
+fi
 
 ##########################################
 # End of CC checks
@@ -6733,6 +6756,7 @@ echo "default devices   $default_devices"
 echo "plugin support    $plugins"
 echo "fuzzing support   $fuzzing"
 echo "gdb               $gdb_bin"
+echo "gpio support      $gpio"
 
 if test "$supported_cpu" = "no"; then
     echo
@@ -7614,6 +7638,10 @@ if test -n "$gdb_bin" ; then
     echo "HAVE_GDB_BIN=$gdb_bin" >> $config_host_mak
 fi
 
+if test "$gpio" = "yes" ; then
+  echo "CONFIG_GPIODEV=y" >> $config_host_mak
+fi
+
 if test "$tcg_interpreter" = "yes"; then
   QEMU_INCLUDES="-iquote \$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"
 elif test "$ARCH" = "sparc64" ; then
diff --git a/include/sysemu/gpiodev.h b/include/sysemu/gpiodev.h
new file mode 100644
index 0000000000000000..bedd141001245207
--- /dev/null
+++ b/include/sysemu/gpiodev.h
@@ -0,0 +1,12 @@
+/*
+ * QEMU GPIO Backend
+ *
+ * Copyright (C) 2018-2020 Glider bv
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/typedefs.h"
+
+void qemu_gpiodev_add(DeviceState *dev, const char *name, unsigned int maxgpio,
+                      Error **errp);
-- 
2.17.1