[PATCH v2 4/8] drm/xen-front: Implement Xen event channel handling

[Oleksandr Andrushchenko <andr2000@gmail.com>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Handle Xen event channels:
  - create for all configured connectors and publish
    corresponding ring references and event channels in Xen store,
    so backend can connect
  - implement event channels interrupt handlers
  - create and destroy event channels with respect to Xen bus state

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
 drivers/gpu/drm/xen/Makefile                |   1 +
 drivers/gpu/drm/xen/xen_drm_front.c         |  12 +-
 drivers/gpu/drm/xen/xen_drm_front.h         |  16 ++
 drivers/gpu/drm/xen/xen_drm_front_evtchnl.c | 381 ++++++++++++++++++++++++++++
 drivers/gpu/drm/xen/xen_drm_front_evtchnl.h |  79 ++++++
 5 files changed, 488 insertions(+), 1 deletion(-)
 create mode 100644 drivers/gpu/drm/xen/xen_drm_front_evtchnl.c
 create mode 100644 drivers/gpu/drm/xen/xen_drm_front_evtchnl.h

diff --git a/drivers/gpu/drm/xen/Makefile b/drivers/gpu/drm/xen/Makefile
index d3ec8c8589e0..8417332f3b58 100644
--- a/drivers/gpu/drm/xen/Makefile
+++ b/drivers/gpu/drm/xen/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0 OR MIT
 
 drm_xen_front-objs := xen_drm_front.o \
+		      xen_drm_front_evtchnl.o \
 		      xen_drm_front_cfg.o
 
 obj-$(CONFIG_DRM_XEN_FRONTEND) += drm_xen_front.o
diff --git a/drivers/gpu/drm/xen/xen_drm_front.c b/drivers/gpu/drm/xen/xen_drm_front.c
index ca42ceb24a40..8312dab862e2 100644
--- a/drivers/gpu/drm/xen/xen_drm_front.c
+++ b/drivers/gpu/drm/xen/xen_drm_front.c
@@ -17,9 +17,11 @@
 #include <xen/interface/io/displif.h>
 
 #include "xen_drm_front.h"
+#include "xen_drm_front_evtchnl.h"
 
 static void xen_drv_remove_internal(struct xen_drm_front_info *front_info)
 {
+	xen_drm_front_evtchnl_free_all(front_info);
 }
 
 static int displback_initwait(struct xen_drm_front_info *front_info)
@@ -33,16 +35,23 @@ static int displback_initwait(struct xen_drm_front_info *front_info)
 		return ret;
 
 	DRM_INFO("Have %d conector(s)\n", cfg->num_connectors);
-	return 0;
+	/* Create event channels for all connectors and publish */
+	ret = xen_drm_front_evtchnl_create_all(front_info);
+	if (ret < 0)
+		return ret;
+
+	return xen_drm_front_evtchnl_publish_all(front_info);
 }
 
 static int displback_connect(struct xen_drm_front_info *front_info)
 {
+	xen_drm_front_evtchnl_set_state(front_info, EVTCHNL_STATE_CONNECTED);
 	return 0;
 }
 
 static void displback_disconnect(struct xen_drm_front_info *front_info)
 {
+	xen_drm_front_evtchnl_set_state(front_info, EVTCHNL_STATE_DISCONNECTED);
 	xenbus_switch_state(front_info->xb_dev, XenbusStateInitialising);
 }
 
@@ -125,6 +134,7 @@ static int xen_drv_probe(struct xenbus_device *xb_dev,
 		return -ENOMEM;
 
 	front_info->xb_dev = xb_dev;
+	spin_lock_init(&front_info->io_lock);
 	dev_set_drvdata(&xb_dev->dev, front_info);
 	return xenbus_switch_state(xb_dev, XenbusStateInitialising);
 }
diff --git a/drivers/gpu/drm/xen/xen_drm_front.h b/drivers/gpu/drm/xen/xen_drm_front.h
index 034a3987657e..4adb6101c889 100644
--- a/drivers/gpu/drm/xen/xen_drm_front.h
+++ b/drivers/gpu/drm/xen/xen_drm_front.h
@@ -13,8 +13,24 @@
 
 #include "xen_drm_front_cfg.h"
 
+#ifndef GRANT_INVALID_REF
+/*
+ * Note on usage of grant reference 0 as invalid grant reference:
+ * grant reference 0 is valid, but never exposed to a PV driver,
+ * because of the fact it is already in use/reserved by the PV console.
+ */
+#define GRANT_INVALID_REF	0
+#endif
+
 struct xen_drm_front_info {
 	struct xenbus_device *xb_dev;
+	/* to protect data between backend IO code and interrupt handler */
+	spinlock_t io_lock;
+	/* virtual DRM platform device */
+	struct platform_device *drm_pdev;
+
+	int num_evt_pairs;
+	struct xen_drm_front_evtchnl_pair *evt_pairs;
 	struct xen_drm_front_cfg cfg;
 };
 
diff --git a/drivers/gpu/drm/xen/xen_drm_front_evtchnl.c b/drivers/gpu/drm/xen/xen_drm_front_evtchnl.c
new file mode 100644
index 000000000000..fd9289a6a1c8
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_front_evtchnl.c
@@ -0,0 +1,381 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ *  Xen para-virtual DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#include <drm/drmP.h>
+
+#include <linux/errno.h>
+#include <linux/irq.h>
+
+#include <xen/xenbus.h>
+#include <xen/events.h>
+#include <xen/grant_table.h>
+
+#include "xen_drm_front.h"
+#include "xen_drm_front_evtchnl.h"
+
+static irqreturn_t evtchnl_interrupt_ctrl(int irq, void *dev_id)
+{
+	struct xen_drm_front_evtchnl *evtchnl = dev_id;
+	struct xen_drm_front_info *front_info = evtchnl->front_info;
+	struct xendispl_resp *resp;
+	RING_IDX i, rp;
+	unsigned long flags;
+
+	if (unlikely(evtchnl->state != EVTCHNL_STATE_CONNECTED))
+		return IRQ_HANDLED;
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+
+again:
+	rp = evtchnl->u.req.ring.sring->rsp_prod;
+	/* ensure we see queued responses up to rp */
+	virt_rmb();
+
+	for (i = evtchnl->u.req.ring.rsp_cons; i != rp; i++) {
+		resp = RING_GET_RESPONSE(&evtchnl->u.req.ring, i);
+		if (unlikely(resp->id != evtchnl->evt_id))
+			continue;
+
+		switch (resp->operation) {
+		case XENDISPL_OP_PG_FLIP:
+		case XENDISPL_OP_FB_ATTACH:
+		case XENDISPL_OP_FB_DETACH:
+		case XENDISPL_OP_DBUF_CREATE:
+		case XENDISPL_OP_DBUF_DESTROY:
+		case XENDISPL_OP_SET_CONFIG:
+			evtchnl->u.req.resp_status = resp->status;
+			complete(&evtchnl->u.req.completion);
+			break;
+
+		default:
+			DRM_ERROR("Operation %d is not supported\n",
+				resp->operation);
+			break;
+		}
+	}
+
+	evtchnl->u.req.ring.rsp_cons = i;
+
+	if (i != evtchnl->u.req.ring.req_prod_pvt) {
+		int more_to_do;
+
+		RING_FINAL_CHECK_FOR_RESPONSES(&evtchnl->u.req.ring,
+				more_to_do);
+		if (more_to_do)
+			goto again;
+	} else
+		evtchnl->u.req.ring.sring->rsp_event = i + 1;
+
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t evtchnl_interrupt_evt(int irq, void *dev_id)
+{
+	struct xen_drm_front_evtchnl *evtchnl = dev_id;
+	struct xen_drm_front_info *front_info = evtchnl->front_info;
+	struct xendispl_event_page *page = evtchnl->u.evt.page;
+	uint32_t cons, prod;
+	unsigned long flags;
+
+	if (unlikely(evtchnl->state != EVTCHNL_STATE_CONNECTED))
+		return IRQ_HANDLED;
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+
+	prod = page->in_prod;
+	/* ensure we see ring contents up to prod */
+	virt_rmb();
+	if (prod == page->in_cons)
+		goto out;
+
+	for (cons = page->in_cons; cons != prod; cons++) {
+		struct xendispl_evt *event;
+
+		event = &XENDISPL_IN_RING_REF(page, cons);
+		if (unlikely(event->id != evtchnl->evt_id++))
+			continue;
+
+		switch (event->type) {
+		case XENDISPL_EVT_PG_FLIP:
+			/* placeholder */
+			break;
+		}
+	}
+	page->in_cons = cons;
+	/* ensure ring contents */
+	virt_wmb();
+
+out:
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+	return IRQ_HANDLED;
+}
+
+static void evtchnl_free(struct xen_drm_front_info *front_info,
+		struct xen_drm_front_evtchnl *evtchnl)
+{
+	unsigned long page = 0;
+
+	if (evtchnl->type == EVTCHNL_TYPE_REQ)
+		page = (unsigned long)evtchnl->u.req.ring.sring;
+	else if (evtchnl->type == EVTCHNL_TYPE_EVT)
+		page = (unsigned long)evtchnl->u.evt.page;
+	if (!page)
+		return;
+
+	evtchnl->state = EVTCHNL_STATE_DISCONNECTED;
+
+	if (evtchnl->type == EVTCHNL_TYPE_REQ) {
+		/* release all who still waits for response if any */
+		evtchnl->u.req.resp_status = -EIO;
+		complete_all(&evtchnl->u.req.completion);
+	}
+
+	if (evtchnl->irq)
+		unbind_from_irqhandler(evtchnl->irq, evtchnl);
+
+	if (evtchnl->port)
+		xenbus_free_evtchn(front_info->xb_dev, evtchnl->port);
+
+	/* end access and free the page */
+	if (evtchnl->gref != GRANT_INVALID_REF)
+		gnttab_end_foreign_access(evtchnl->gref, 0, page);
+
+	memset(evtchnl, 0, sizeof(*evtchnl));
+}
+
+static int evtchnl_alloc(struct xen_drm_front_info *front_info, int index,
+		struct xen_drm_front_evtchnl *evtchnl,
+		enum xen_drm_front_evtchnl_type type)
+{
+	struct xenbus_device *xb_dev = front_info->xb_dev;
+	unsigned long page;
+	grant_ref_t gref;
+	irq_handler_t handler;
+	int ret;
+
+	memset(evtchnl, 0, sizeof(*evtchnl));
+	evtchnl->type = type;
+	evtchnl->index = index;
+	evtchnl->front_info = front_info;
+	evtchnl->state = EVTCHNL_STATE_DISCONNECTED;
+	evtchnl->gref = GRANT_INVALID_REF;
+
+	page = get_zeroed_page(GFP_NOIO | __GFP_HIGH);
+	if (!page) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	if (type == EVTCHNL_TYPE_REQ) {
+		struct xen_displif_sring *sring;
+
+		init_completion(&evtchnl->u.req.completion);
+		sring = (struct xen_displif_sring *)page;
+		SHARED_RING_INIT(sring);
+		FRONT_RING_INIT(&evtchnl->u.req.ring,
+				sring, XEN_PAGE_SIZE);
+
+		ret = xenbus_grant_ring(xb_dev, sring, 1, &gref);
+		if (ret < 0)
+			goto fail;
+
+		handler = evtchnl_interrupt_ctrl;
+	} else {
+		evtchnl->u.evt.page = (struct xendispl_event_page *)page;
+
+		ret = gnttab_grant_foreign_access(xb_dev->otherend_id,
+				virt_to_gfn((void *)page), 0);
+		if (ret < 0)
+			goto fail;
+
+		gref = ret;
+		handler = evtchnl_interrupt_evt;
+	}
+	evtchnl->gref = gref;
+
+	ret = xenbus_alloc_evtchn(xb_dev, &evtchnl->port);
+	if (ret < 0)
+		goto fail;
+
+	ret = bind_evtchn_to_irqhandler(evtchnl->port,
+			handler, 0, xb_dev->devicetype, evtchnl);
+	if (ret < 0)
+		goto fail;
+
+	evtchnl->irq = ret;
+	return 0;
+
+fail:
+	DRM_ERROR("Failed to allocate ring: %d\n", ret);
+	return ret;
+}
+
+int xen_drm_front_evtchnl_create_all(struct xen_drm_front_info *front_info)
+{
+	struct xen_drm_front_cfg *cfg;
+	int ret, conn;
+
+	cfg = &front_info->cfg;
+
+	front_info->evt_pairs = devm_kcalloc(&front_info->xb_dev->dev,
+			cfg->num_connectors,
+			sizeof(struct xen_drm_front_evtchnl_pair), GFP_KERNEL);
+	if (!front_info->evt_pairs) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	for (conn = 0; conn < cfg->num_connectors; conn++) {
+		ret = evtchnl_alloc(front_info, conn,
+				&front_info->evt_pairs[conn].req,
+				EVTCHNL_TYPE_REQ);
+		if (ret < 0) {
+			DRM_ERROR("Error allocating control channel\n");
+			goto fail;
+		}
+
+		ret = evtchnl_alloc(front_info, conn,
+				&front_info->evt_pairs[conn].evt,
+				EVTCHNL_TYPE_EVT);
+		if (ret < 0) {
+			DRM_ERROR("Error allocating in-event channel\n");
+			goto fail;
+		}
+	}
+	front_info->num_evt_pairs = cfg->num_connectors;
+	return 0;
+
+fail:
+	xen_drm_front_evtchnl_free_all(front_info);
+	return ret;
+}
+
+static int evtchnl_publish(struct xenbus_transaction xbt,
+		struct xen_drm_front_evtchnl *evtchnl, const char *path,
+		const char *node_ring, const char *node_chnl)
+{
+	struct xenbus_device *xb_dev = evtchnl->front_info->xb_dev;
+	int ret;
+
+	/* write control channel ring reference */
+	ret = xenbus_printf(xbt, path, node_ring, "%u", evtchnl->gref);
+	if (ret < 0) {
+		xenbus_dev_error(xb_dev, ret, "writing ring-ref");
+		return ret;
+	}
+
+	/* write event channel ring reference */
+	ret = xenbus_printf(xbt, path, node_chnl, "%u", evtchnl->port);
+	if (ret < 0) {
+		xenbus_dev_error(xb_dev, ret, "writing event channel");
+		return ret;
+	}
+
+	return 0;
+}
+
+int xen_drm_front_evtchnl_publish_all(struct xen_drm_front_info *front_info)
+{
+	struct xenbus_transaction xbt;
+	struct xen_drm_front_cfg *plat_data;
+	int ret, conn;
+
+	plat_data = &front_info->cfg;
+
+again:
+	ret = xenbus_transaction_start(&xbt);
+	if (ret < 0) {
+		xenbus_dev_fatal(front_info->xb_dev, ret,
+				"starting transaction");
+		return ret;
+	}
+
+	for (conn = 0; conn < plat_data->num_connectors; conn++) {
+		ret = evtchnl_publish(xbt,
+				&front_info->evt_pairs[conn].req,
+				plat_data->connectors[conn].xenstore_path,
+				XENDISPL_FIELD_REQ_RING_REF,
+				XENDISPL_FIELD_REQ_CHANNEL);
+		if (ret < 0)
+			goto fail;
+
+		ret = evtchnl_publish(xbt,
+				&front_info->evt_pairs[conn].evt,
+				plat_data->connectors[conn].xenstore_path,
+				XENDISPL_FIELD_EVT_RING_REF,
+				XENDISPL_FIELD_EVT_CHANNEL);
+		if (ret < 0)
+			goto fail;
+	}
+
+	ret = xenbus_transaction_end(xbt, 0);
+	if (ret < 0) {
+		if (ret == -EAGAIN)
+			goto again;
+
+		xenbus_dev_fatal(front_info->xb_dev, ret,
+				"completing transaction");
+		goto fail_to_end;
+	}
+
+	return 0;
+
+fail:
+	xenbus_transaction_end(xbt, 1);
+
+fail_to_end:
+	xenbus_dev_fatal(front_info->xb_dev, ret, "writing Xen store");
+	return ret;
+}
+
+void xen_drm_front_evtchnl_flush(struct xen_drm_front_evtchnl *evtchnl)
+{
+	int notify;
+
+	evtchnl->u.req.ring.req_prod_pvt++;
+	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&evtchnl->u.req.ring, notify);
+	if (notify)
+		notify_remote_via_irq(evtchnl->irq);
+}
+
+void xen_drm_front_evtchnl_set_state(struct xen_drm_front_info *front_info,
+		enum xen_drm_front_evtchnl_state state)
+{
+	unsigned long flags;
+	int i;
+
+	if (!front_info->evt_pairs)
+		return;
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+	for (i = 0; i < front_info->num_evt_pairs; i++) {
+		front_info->evt_pairs[i].req.state = state;
+		front_info->evt_pairs[i].evt.state = state;
+	}
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+}
+
+void xen_drm_front_evtchnl_free_all(struct xen_drm_front_info *front_info)
+{
+	int i;
+
+	if (!front_info->evt_pairs)
+		return;
+
+	for (i = 0; i < front_info->num_evt_pairs; i++) {
+		evtchnl_free(front_info, &front_info->evt_pairs[i].req);
+		evtchnl_free(front_info, &front_info->evt_pairs[i].evt);
+	}
+
+	devm_kfree(&front_info->xb_dev->dev, front_info->evt_pairs);
+	front_info->evt_pairs = NULL;
+}
diff --git a/drivers/gpu/drm/xen/xen_drm_front_evtchnl.h b/drivers/gpu/drm/xen/xen_drm_front_evtchnl.h
new file mode 100644
index 000000000000..8faacf9444e6
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_front_evtchnl.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+/*
+ *  Xen para-virtual DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#ifndef __XEN_DRM_FRONT_EVTCHNL_H_
+#define __XEN_DRM_FRONT_EVTCHNL_H_
+
+#include <linux/completion.h>
+#include <linux/types.h>
+
+#include <xen/interface/io/ring.h>
+#include <xen/interface/io/displif.h>
+
+/*
+ * All operations which are not connector oriented use this ctrl event channel,
+ * e.g. fb_attach/destroy which belong to a DRM device, not to a CRTC.
+ */
+#define GENERIC_OP_EVT_CHNL	0
+
+enum xen_drm_front_evtchnl_state {
+	EVTCHNL_STATE_DISCONNECTED,
+	EVTCHNL_STATE_CONNECTED,
+};
+
+enum xen_drm_front_evtchnl_type {
+	EVTCHNL_TYPE_REQ,
+	EVTCHNL_TYPE_EVT,
+};
+
+struct xen_drm_front_drm_info;
+
+struct xen_drm_front_evtchnl {
+	struct xen_drm_front_info *front_info;
+	int gref;
+	int port;
+	int irq;
+	int index;
+	enum xen_drm_front_evtchnl_state state;
+	enum xen_drm_front_evtchnl_type type;
+	/* either response id or incoming event id */
+	uint16_t evt_id;
+	/* next request id or next expected event id */
+	uint16_t evt_next_id;
+	union {
+		struct {
+			struct xen_displif_front_ring ring;
+			struct completion completion;
+			/* latest response status */
+			int resp_status;
+		} req;
+		struct {
+			struct xendispl_event_page *page;
+		} evt;
+	} u;
+};
+
+struct xen_drm_front_evtchnl_pair {
+	struct xen_drm_front_evtchnl req;
+	struct xen_drm_front_evtchnl evt;
+};
+
+int xen_drm_front_evtchnl_create_all(struct xen_drm_front_info *front_info);
+
+int xen_drm_front_evtchnl_publish_all(struct xen_drm_front_info *front_info);
+
+void xen_drm_front_evtchnl_flush(struct xen_drm_front_evtchnl *evtchnl);
+
+void xen_drm_front_evtchnl_set_state(struct xen_drm_front_info *front_info,
+		enum xen_drm_front_evtchnl_state state);
+
+void xen_drm_front_evtchnl_free_all(struct xen_drm_front_info *front_info);
+
+#endif /* __XEN_DRM_FRONT_EVTCHNL_H_ */
-- 
2.7.4

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