ALSA: xen-front: Introduce Xen para-virtualized sound frontend driver

Introduce skeleton of the para-virtualized Xen sound
frontend driver.

Initial handling for Xen bus states: implement
Xen bus state machine for the frontend driver according to
the state diagram and recovery flow from sound para-virtualized
protocol: xen/interface/io/sndif.h.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

6 files changed, 232 insertions, 1 deletions

diff --git a/sound/Kconfig b/sound/Kconfig
index 6833db9002ec..1140e9988fc5 100644
--- a/sound/Kconfig
+++ b/sound/Kconfig
@@ -96,6 +96,8 @@ source "sound/x86/Kconfig"
 
 source "sound/synth/Kconfig"
 
+source "sound/xen/Kconfig"
+
 endif # SND
 
 endif # !UML
diff --git a/sound/Makefile b/sound/Makefile
index 99d8c31262c8..797ecdcd35e2 100644
--- a/sound/Makefile
+++ b/sound/Makefile
@@ -5,7 +5,7 @@
 obj-$(CONFIG_SOUND) += soundcore.o
 obj-$(CONFIG_DMASOUND) += oss/dmasound/
 obj-$(CONFIG_SND) += core/ i2c/ drivers/ isa/ pci/ ppc/ arm/ sh/ synth/ usb/ \
-        firewire/ sparc/ spi/ parisc/ pcmcia/ mips/ soc/ atmel/ hda/ x86/
+        firewire/ sparc/ spi/ parisc/ pcmcia/ mips/ soc/ atmel/ hda/ x86/ xen/
 obj-$(CONFIG_SND_AOA) += aoa/
 
 # This one must be compilable even if sound is configured out
diff --git a/sound/xen/Kconfig b/sound/xen/Kconfig
new file mode 100644
index 000000000000..4f1fceea82d2
--- /dev/null
+++ b/sound/xen/Kconfig
@@ -0,0 +1,10 @@
+# ALSA Xen drivers
+
+config SND_XEN_FRONTEND
+        tristate "Xen para-virtualized sound frontend driver"
+        depends on XEN
+        select SND_PCM
+        select XEN_XENBUS_FRONTEND
+        help
+          Choose this option if you want to enable a para-virtualized
+          frontend sound driver for Xen guest OSes.
diff --git a/sound/xen/Makefile b/sound/xen/Makefile
new file mode 100644
index 000000000000..4507ef3c27fd
--- /dev/null
+++ b/sound/xen/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0 OR MIT
+
+snd_xen_front-objs := xen_snd_front.o
+
+obj-$(CONFIG_SND_XEN_FRONTEND) += snd_xen_front.o
diff --git a/sound/xen/xen_snd_front.c b/sound/xen/xen_snd_front.c
new file mode 100644
index 000000000000..bbbe2767b565
--- /dev/null
+++ b/sound/xen/xen_snd_front.c
@@ -0,0 +1,196 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#include <linux/delay.h>
+#include <linux/module.h>
+
+#include <xen/platform_pci.h>
+#include <xen/xen.h>
+#include <xen/xenbus.h>
+
+#include <xen/interface/io/sndif.h>
+
+#include "xen_snd_front.h"
+
+static void xen_snd_drv_fini(struct xen_snd_front_info *front_info)
+{
+}
+
+static int sndback_initwait(struct xen_snd_front_info *front_info)
+{
+        return 0;
+}
+
+static int sndback_connect(struct xen_snd_front_info *front_info)
+{
+        return 0;
+}
+
+static void sndback_disconnect(struct xen_snd_front_info *front_info)
+{
+        xen_snd_drv_fini(front_info);
+        xenbus_switch_state(front_info->xb_dev, XenbusStateInitialising);
+}
+
+static void sndback_changed(struct xenbus_device *xb_dev,
+                            enum xenbus_state backend_state)
+{
+        struct xen_snd_front_info *front_info = dev_get_drvdata(&xb_dev->dev);
+        int ret;
+
+        dev_dbg(&xb_dev->dev, "Backend state is %s, front is %s\n",
+                xenbus_strstate(backend_state),
+                xenbus_strstate(xb_dev->state));
+
+        switch (backend_state) {
+        case XenbusStateReconfiguring:
+                /* fall through */
+        case XenbusStateReconfigured:
+                /* fall through */
+        case XenbusStateInitialised:
+                /* fall through */
+                break;
+
+        case XenbusStateInitialising:
+                /* Recovering after backend unexpected closure. */
+                sndback_disconnect(front_info);
+                break;
+
+        case XenbusStateInitWait:
+                /* Recovering after backend unexpected closure. */
+                sndback_disconnect(front_info);
+
+                ret = sndback_initwait(front_info);
+                if (ret < 0)
+                        xenbus_dev_fatal(xb_dev, ret, "initializing frontend");
+                else
+                        xenbus_switch_state(xb_dev, XenbusStateInitialised);
+                break;
+
+        case XenbusStateConnected:
+                if (xb_dev->state != XenbusStateInitialised)
+                        break;
+
+                ret = sndback_connect(front_info);
+                if (ret < 0)
+                        xenbus_dev_fatal(xb_dev, ret, "initializing frontend");
+                else
+                        xenbus_switch_state(xb_dev, XenbusStateConnected);
+                break;
+
+        case XenbusStateClosing:
+                /*
+                 * In this state backend starts freeing resources,
+                 * so let it go into closed state first, so we can also
+                 * remove ours.
+                 */
+                break;
+
+        case XenbusStateUnknown:
+                /* fall through */
+        case XenbusStateClosed:
+                if (xb_dev->state == XenbusStateClosed)
+                        break;
+
+                sndback_disconnect(front_info);
+                break;
+        }
+}
+
+static int xen_drv_probe(struct xenbus_device *xb_dev,
+                         const struct xenbus_device_id *id)
+{
+        struct xen_snd_front_info *front_info;
+
+        front_info = devm_kzalloc(&xb_dev->dev,
+                                  sizeof(*front_info), GFP_KERNEL);
+        if (!front_info)
+                return -ENOMEM;
+
+        front_info->xb_dev = xb_dev;
+        dev_set_drvdata(&xb_dev->dev, front_info);
+
+        return xenbus_switch_state(xb_dev, XenbusStateInitialising);
+}
+
+static int xen_drv_remove(struct xenbus_device *dev)
+{
+        struct xen_snd_front_info *front_info = dev_get_drvdata(&dev->dev);
+        int to = 100;
+
+        xenbus_switch_state(dev, XenbusStateClosing);
+
+        /*
+         * On driver removal it is disconnected from XenBus,
+         * so no backend state change events come via .otherend_changed
+         * callback. This prevents us from exiting gracefully, e.g.
+         * signaling the backend to free event channels, waiting for its
+         * state to change to XenbusStateClosed and cleaning at our end.
+         * Normally when front driver removed backend will finally go into
+         * XenbusStateInitWait state.
+         *
+         * Workaround: read backend's state manually and wait with time-out.
+         */
+        while ((xenbus_read_unsigned(front_info->xb_dev->otherend, "state",
+                                     XenbusStateUnknown) != XenbusStateInitWait) &&
+                                     to--)
+                msleep(10);
+
+        if (!to) {
+                unsigned int state;
+
+                state = xenbus_read_unsigned(front_info->xb_dev->otherend,
+                                             "state", XenbusStateUnknown);
+                pr_err("Backend state is %s while removing driver\n",
+                       xenbus_strstate(state));
+        }
+
+        xen_snd_drv_fini(front_info);
+        xenbus_frontend_closed(dev);
+        return 0;
+}
+
+static const struct xenbus_device_id xen_drv_ids[] = {
+        { XENSND_DRIVER_NAME },
+        { "" }
+};
+
+static struct xenbus_driver xen_driver = {
+        .ids = xen_drv_ids,
+        .probe = xen_drv_probe,
+        .remove = xen_drv_remove,
+        .otherend_changed = sndback_changed,
+};
+
+static int __init xen_drv_init(void)
+{
+        if (!xen_domain())
+                return -ENODEV;
+
+        if (!xen_has_pv_devices())
+                return -ENODEV;
+
+        pr_info("Initialising Xen " XENSND_DRIVER_NAME " frontend driver\n");
+        return xenbus_register_frontend(&xen_driver);
+}
+
+static void __exit xen_drv_fini(void)
+{
+        pr_info("Unregistering Xen " XENSND_DRIVER_NAME " frontend driver\n");
+        xenbus_unregister_driver(&xen_driver);
+}
+
+module_init(xen_drv_init);
+module_exit(xen_drv_fini);
+
+MODULE_DESCRIPTION("Xen virtual sound device frontend");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("xen:" XENSND_DRIVER_NAME);
+MODULE_SUPPORTED_DEVICE("{{ALSA,Virtual soundcard}}");
diff --git a/sound/xen/xen_snd_front.h b/sound/xen/xen_snd_front.h
new file mode 100644
index 000000000000..4ae204b23d32
--- /dev/null
+++ b/sound/xen/xen_snd_front.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#ifndef __XEN_SND_FRONT_H
+#define __XEN_SND_FRONT_H
+
+struct xen_snd_front_info {
+        struct xenbus_device *xb_dev;
+};
+
+#endif /* __XEN_SND_FRONT_H */