drm/xen-front: Add support for Xen PV display frontend

Add support for Xen para-virtualized frontend display driver.
Accompanying backend [1] is implemented as a user-space application
and its helper library [2], capable of running as a Weston client
or DRM master.
Configuration of both backend and frontend is done via
Xen guest domain configuration options [3].

Driver limitations:
 1. Only primary plane without additional properties is supported.
 2. Only one video mode supported which resolution is configured
    via XenStore.
 3. All CRTCs operate at fixed frequency of 60Hz.

1. Implement Xen bus state machine for the frontend driver according to
the state diagram and recovery flow from display para-virtualized
protocol: xen/interface/io/displif.h.

2. Read configuration values from Xen store according
to xen/interface/io/displif.h protocol:
  - read connector(s) configuration
  - read buffer allocation mode (backend/frontend)

3. 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

4. Implement shared buffer handling according to the
para-virtualized display device protocol at xen/interface/io/displif.h:
  - handle page directories according to displif protocol:
    - allocate and share page directories
    - grant references to the required set of pages for the
      page directory
  - allocate xen balllooned pages via Xen balloon driver
    with alloc_xenballooned_pages/free_xenballooned_pages
  - grant references to the required set of pages for the
    shared buffer itself
  - implement pages map/unmap for the buffers allocated by the
    backend (gnttab_map_refs/gnttab_unmap_refs)

5. Implement kernel modesetiing/connector handling using
DRM simple KMS helper pipeline:

- implement KMS part of the driver with the help of DRM
  simple pipepline helper which is possible due to the fact
  that the para-virtualized driver only supports a single
  (primary) plane:
  - initialize connectors according to XenStore configuration
  - handle frame done events from the backend
  - create and destroy frame buffers and propagate those
    to the backend
  - propagate set/reset mode configuration to the backend on display
    enable/disable callbacks
  - send page flip request to the backend and implement logic for
    reporting backend IO errors on prepare fb callback

- implement virtual connector handling:
  - support only pixel formats suitable for single plane modes
  - make sure the connector is always connected
  - support a single video mode as per para-virtualized driver
    configuration

6. Implement GEM handling depending on driver mode of operation:
depending on the requirements for the para-virtualized environment,
namely requirements dictated by the accompanying DRM/(v)GPU drivers
running in both host and guest environments, number of operating
modes of para-virtualized display driver are supported:
 - display buffers can be allocated by either
   frontend driver or backend
 - display buffers can be allocated to be contiguous
   in memory or not

Note! Frontend driver itself has no dependency on contiguous memory for
its operation.

6.1. Buffers allocated by the frontend driver.

The below modes of operation are configured at compile-time via
frontend driver's kernel configuration.

6.1.1. Front driver configured to use GEM CMA helpers
     This use-case is useful when used with accompanying DRM/vGPU driver
     in guest domain which was designed to only work with contiguous
     buffers, e.g. DRM driver based on GEM CMA helpers: such drivers can
     only import contiguous PRIME buffers, thus requiring frontend driver
     to provide such. In order to implement this mode of operation
     para-virtualized frontend driver can be configured to use
     GEM CMA helpers.

6.1.2. Front driver doesn't use GEM CMA
     If accompanying drivers can cope with non-contiguous memory then, to
     lower pressure on CMA subsystem of the kernel, driver can allocate
     buffers from system memory.

Note! If used with accompanying DRM/(v)GPU drivers this mode of operation
may require IOMMU support on the platform, so accompanying DRM/vGPU
hardware can still reach display buffer memory while importing PRIME
buffers from the frontend driver.

6.2. Buffers allocated by the backend

This mode of operation is run-time configured via guest domain
configuration through XenStore entries.

For systems which do not provide IOMMU support, but having specific
requirements for display buffers it is possible to allocate such buffers
at backend side and share those with the frontend.
For example, if host domain is 1:1 mapped and has DRM/GPU hardware
expecting physically contiguous memory, this allows implementing
zero-copying use-cases.

Note, while using this scenario the following should be considered:
  a) If guest domain dies then pages/grants received from the backend
     cannot be claimed back
  b) Misbehaving guest may send too many requests to the
     backend exhausting its grant references and memory
     (consider this from security POV).

Note! Configuration options 1.1 (contiguous display buffers) and 2
(backend allocated buffers) are not supported at the same time.

7. Handle communication with the backend:
 - send requests and wait for the responses according
   to the displif protocol
 - serialize access to the communication channel
 - time-out used for backend communication is set to 3000 ms
 - manage display buffers shared with the backend

[1] https://github.com/xen-troops/displ_be
[2] https://github.com/xen-troops/libxenbe
[3] https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/man/xl.cfg.pod.5.in;h=a699367779e2ae1212ff8f638eff0206ec1a1cc9;hb=refs/heads/master#l1257

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180403112317.28751-2-andr2000@gmail.com

1 files changed, 372 insertions, 0 deletions

diff --git a/drivers/gpu/drm/xen/xen_drm_front_kms.c b/drivers/gpu/drm/xen/xen_drm_front_kms.c
new file mode 100644
index 000000000000..0bd6681fa4f3
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_front_kms.c
@@ -0,0 +1,372 @@
+// 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 "xen_drm_front_kms.h"
+
+#include <drm/drmP.h>
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_crtc_helper.h>
+#include <drm/drm_gem.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+
+#include "xen_drm_front.h"
+#include "xen_drm_front_conn.h"
+
+/*
+ * Timeout in ms to wait for frame done event from the backend:
+ * must be a bit more than IO time-out
+ */
+#define FRAME_DONE_TO_MS	(XEN_DRM_FRONT_WAIT_BACK_MS + 100)
+
+static struct xen_drm_front_drm_pipeline *
+to_xen_drm_pipeline(struct drm_simple_display_pipe *pipe)
+{
+	return container_of(pipe, struct xen_drm_front_drm_pipeline, pipe);
+}
+
+static void fb_destroy(struct drm_framebuffer *fb)
+{
+	struct xen_drm_front_drm_info *drm_info = fb->dev->dev_private;
+	int idx;
+
+	if (drm_dev_enter(fb->dev, &idx)) {
+		xen_drm_front_fb_detach(drm_info->front_info,
+					xen_drm_front_fb_to_cookie(fb));
+		drm_dev_exit(idx);
+	}
+	drm_gem_fb_destroy(fb);
+}
+
+static struct drm_framebuffer_funcs fb_funcs = {
+	.destroy = fb_destroy,
+};
+
+static struct drm_framebuffer *
+fb_create(struct drm_device *dev, struct drm_file *filp,
+	  const struct drm_mode_fb_cmd2 *mode_cmd)
+{
+	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
+	static struct drm_framebuffer *fb;
+	struct drm_gem_object *gem_obj;
+	int ret;
+
+	fb = drm_gem_fb_create_with_funcs(dev, filp, mode_cmd, &fb_funcs);
+	if (IS_ERR_OR_NULL(fb))
+		return fb;
+
+	gem_obj = drm_gem_object_lookup(filp, mode_cmd->handles[0]);
+	if (!gem_obj) {
+		DRM_ERROR("Failed to lookup GEM object\n");
+		ret = -ENOENT;
+		goto fail;
+	}
+
+	drm_gem_object_put_unlocked(gem_obj);
+
+	ret = xen_drm_front_fb_attach(drm_info->front_info,
+				      xen_drm_front_dbuf_to_cookie(gem_obj),
+				      xen_drm_front_fb_to_cookie(fb),
+				      fb->width, fb->height,
+				      fb->format->format);
+	if (ret < 0) {
+		DRM_ERROR("Back failed to attach FB %p: %d\n", fb, ret);
+		goto fail;
+	}
+
+	return fb;
+
+fail:
+	drm_gem_fb_destroy(fb);
+	return ERR_PTR(ret);
+}
+
+static const struct drm_mode_config_funcs mode_config_funcs = {
+	.fb_create = fb_create,
+	.atomic_check = drm_atomic_helper_check,
+	.atomic_commit = drm_atomic_helper_commit,
+};
+
+static void send_pending_event(struct xen_drm_front_drm_pipeline *pipeline)
+{
+	struct drm_crtc *crtc = &pipeline->pipe.crtc;
+	struct drm_device *dev = crtc->dev;
+	unsigned long flags;
+
+	spin_lock_irqsave(&dev->event_lock, flags);
+	if (pipeline->pending_event)
+		drm_crtc_send_vblank_event(crtc, pipeline->pending_event);
+	pipeline->pending_event = NULL;
+	spin_unlock_irqrestore(&dev->event_lock, flags);
+}
+
+static void display_enable(struct drm_simple_display_pipe *pipe,
+			   struct drm_crtc_state *crtc_state,
+			   struct drm_plane_state *plane_state)
+{
+	struct xen_drm_front_drm_pipeline *pipeline =
+			to_xen_drm_pipeline(pipe);
+	struct drm_crtc *crtc = &pipe->crtc;
+	struct drm_framebuffer *fb = plane_state->fb;
+	int ret, idx;
+
+	if (!drm_dev_enter(pipe->crtc.dev, &idx))
+		return;
+
+	ret = xen_drm_front_mode_set(pipeline, crtc->x, crtc->y,
+				     fb->width, fb->height,
+				     fb->format->cpp[0] * 8,
+				     xen_drm_front_fb_to_cookie(fb));
+
+	if (ret) {
+		DRM_ERROR("Failed to enable display: %d\n", ret);
+		pipeline->conn_connected = false;
+	}
+
+	drm_dev_exit(idx);
+}
+
+static void display_disable(struct drm_simple_display_pipe *pipe)
+{
+	struct xen_drm_front_drm_pipeline *pipeline =
+			to_xen_drm_pipeline(pipe);
+	int ret = 0, idx;
+
+	if (drm_dev_enter(pipe->crtc.dev, &idx)) {
+		ret = xen_drm_front_mode_set(pipeline, 0, 0, 0, 0, 0,
+					     xen_drm_front_fb_to_cookie(NULL));
+		drm_dev_exit(idx);
+	}
+	if (ret)
+		DRM_ERROR("Failed to disable display: %d\n", ret);
+
+	/* Make sure we can restart with enabled connector next time */
+	pipeline->conn_connected = true;
+
+	/* release stalled event if any */
+	send_pending_event(pipeline);
+}
+
+void xen_drm_front_kms_on_frame_done(struct xen_drm_front_drm_pipeline *pipeline,
+				     u64 fb_cookie)
+{
+	/*
+	 * This runs in interrupt context, e.g. under
+	 * drm_info->front_info->io_lock, so we cannot call _sync version
+	 * to cancel the work
+	 */
+	cancel_delayed_work(&pipeline->pflip_to_worker);
+
+	send_pending_event(pipeline);
+}
+
+static void pflip_to_worker(struct work_struct *work)
+{
+	struct delayed_work *delayed_work = to_delayed_work(work);
+	struct xen_drm_front_drm_pipeline *pipeline =
+			container_of(delayed_work,
+				     struct xen_drm_front_drm_pipeline,
+				     pflip_to_worker);
+
+	DRM_ERROR("Frame done timed-out, releasing");
+	send_pending_event(pipeline);
+}
+
+static bool display_send_page_flip(struct drm_simple_display_pipe *pipe,
+				   struct drm_plane_state *old_plane_state)
+{
+	struct drm_plane_state *plane_state =
+			drm_atomic_get_new_plane_state(old_plane_state->state,
+						       &pipe->plane);
+
+	/*
+	 * If old_plane_state->fb is NULL and plane_state->fb is not,
+	 * then this is an atomic commit which will enable display.
+	 * If old_plane_state->fb is not NULL and plane_state->fb is,
+	 * then this is an atomic commit which will disable display.
+	 * Ignore these and do not send page flip as this framebuffer will be
+	 * sent to the backend as a part of display_set_config call.
+	 */
+	if (old_plane_state->fb && plane_state->fb) {
+		struct xen_drm_front_drm_pipeline *pipeline =
+				to_xen_drm_pipeline(pipe);
+		struct xen_drm_front_drm_info *drm_info = pipeline->drm_info;
+		int ret;
+
+		schedule_delayed_work(&pipeline->pflip_to_worker,
+				      msecs_to_jiffies(FRAME_DONE_TO_MS));
+
+		ret = xen_drm_front_page_flip(drm_info->front_info,
+					      pipeline->index,
+					      xen_drm_front_fb_to_cookie(plane_state->fb));
+		if (ret) {
+			DRM_ERROR("Failed to send page flip request to backend: %d\n", ret);
+
+			pipeline->conn_connected = false;
+			/*
+			 * Report the flip not handled, so pending event is
+			 * sent, unblocking user-space.
+			 */
+			return false;
+		}
+		/*
+		 * Signal that page flip was handled, pending event will be sent
+		 * on frame done event from the backend.
+		 */
+		return true;
+	}
+
+	return false;
+}
+
+static int display_prepare_fb(struct drm_simple_display_pipe *pipe,
+			      struct drm_plane_state *plane_state)
+{
+	return drm_gem_fb_prepare_fb(&pipe->plane, plane_state);
+}
+
+static void display_update(struct drm_simple_display_pipe *pipe,
+			   struct drm_plane_state *old_plane_state)
+{
+	struct xen_drm_front_drm_pipeline *pipeline =
+			to_xen_drm_pipeline(pipe);
+	struct drm_crtc *crtc = &pipe->crtc;
+	struct drm_pending_vblank_event *event;
+	int idx;
+
+	event = crtc->state->event;
+	if (event) {
+		struct drm_device *dev = crtc->dev;
+		unsigned long flags;
+
+		WARN_ON(pipeline->pending_event);
+
+		spin_lock_irqsave(&dev->event_lock, flags);
+		crtc->state->event = NULL;
+
+		pipeline->pending_event = event;
+		spin_unlock_irqrestore(&dev->event_lock, flags);
+	}
+
+	if (!drm_dev_enter(pipe->crtc.dev, &idx)) {
+		send_pending_event(pipeline);
+		return;
+	}
+
+	/*
+	 * Send page flip request to the backend *after* we have event cached
+	 * above, so on page flip done event from the backend we can
+	 * deliver it and there is no race condition between this code and
+	 * event from the backend.
+	 * If this is not a page flip, e.g. no flip done event from the backend
+	 * is expected, then send now.
+	 */
+	if (!display_send_page_flip(pipe, old_plane_state))
+		send_pending_event(pipeline);
+
+	drm_dev_exit(idx);
+}
+
+static enum drm_mode_status
+display_mode_valid(struct drm_crtc *crtc, const struct drm_display_mode *mode)
+{
+	struct xen_drm_front_drm_pipeline *pipeline =
+			container_of(crtc, struct xen_drm_front_drm_pipeline,
+				     pipe.crtc);
+
+	if (mode->hdisplay != pipeline->width)
+		return MODE_ERROR;
+
+	if (mode->vdisplay != pipeline->height)
+		return MODE_ERROR;
+
+	return MODE_OK;
+}
+
+static const struct drm_simple_display_pipe_funcs display_funcs = {
+	.mode_valid = display_mode_valid,
+	.enable = display_enable,
+	.disable = display_disable,
+	.prepare_fb = display_prepare_fb,
+	.update = display_update,
+};
+
+static int display_pipe_init(struct xen_drm_front_drm_info *drm_info,
+			     int index, struct xen_drm_front_cfg_connector *cfg,
+			     struct xen_drm_front_drm_pipeline *pipeline)
+{
+	struct drm_device *dev = drm_info->drm_dev;
+	const u32 *formats;
+	int format_count;
+	int ret;
+
+	pipeline->drm_info = drm_info;
+	pipeline->index = index;
+	pipeline->height = cfg->height;
+	pipeline->width = cfg->width;
+
+	INIT_DELAYED_WORK(&pipeline->pflip_to_worker, pflip_to_worker);
+
+	ret = xen_drm_front_conn_init(drm_info, &pipeline->conn);
+	if (ret)
+		return ret;
+
+	formats = xen_drm_front_conn_get_formats(&format_count);
+
+	return drm_simple_display_pipe_init(dev, &pipeline->pipe,
+					    &display_funcs, formats,
+					    format_count, NULL,
+					    &pipeline->conn);
+}
+
+int xen_drm_front_kms_init(struct xen_drm_front_drm_info *drm_info)
+{
+	struct drm_device *dev = drm_info->drm_dev;
+	int i, ret;
+
+	drm_mode_config_init(dev);
+
+	dev->mode_config.min_width = 0;
+	dev->mode_config.min_height = 0;
+	dev->mode_config.max_width = 4095;
+	dev->mode_config.max_height = 2047;
+	dev->mode_config.funcs = &mode_config_funcs;
+
+	for (i = 0; i < drm_info->front_info->cfg.num_connectors; i++) {
+		struct xen_drm_front_cfg_connector *cfg =
+				&drm_info->front_info->cfg.connectors[i];
+		struct xen_drm_front_drm_pipeline *pipeline =
+				&drm_info->pipeline[i];
+
+		ret = display_pipe_init(drm_info, i, cfg, pipeline);
+		if (ret) {
+			drm_mode_config_cleanup(dev);
+			return ret;
+		}
+	}
+
+	drm_mode_config_reset(dev);
+	drm_kms_helper_poll_init(dev);
+	return 0;
+}
+
+void xen_drm_front_kms_fini(struct xen_drm_front_drm_info *drm_info)
+{
+	int i;
+
+	for (i = 0; i < drm_info->front_info->cfg.num_connectors; i++) {
+		struct xen_drm_front_drm_pipeline *pipeline =
+				&drm_info->pipeline[i];
+
+		cancel_delayed_work_sync(&pipeline->pflip_to_worker);
+
+		send_pending_event(pipeline);
+	}
+}