Add zero-copy driver

Documentation/gpu/index.rst

@@ -19,6 +19,8 @@ Linux GPU Driver Developer's Guide
    vga-switcheroo
    vgaarbiter
    bridge/dw-hdmi
+   xen-front
+   xen-zcopy
    todo
 
 .. only::  subproject and html

Documentation/gpu/xen-front.rst

@@ -0,0 +1,31 @@
+====================================================
+ drm/xen-front Xen para-virtualized frontend driver
+====================================================
+
+This frontend driver implements Xen para-virtualized display
+according to the display protocol described at
+include/xen/interface/io/displif.h
+
+Driver modes of operation in terms of display buffers used
+==========================================================
+
+.. kernel-doc:: drivers/gpu/drm/xen/xen_drm_front.h
+   :doc: Driver modes of operation in terms of display buffers used
+
+Buffers allocated by the frontend driver
+----------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/xen/xen_drm_front.h
+   :doc: Buffers allocated by the frontend driver
+
+Buffers allocated by the backend
+--------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/xen/xen_drm_front.h
+   :doc: Buffers allocated by the backend
+
+Driver limitations
+==================
+
+.. kernel-doc:: drivers/gpu/drm/xen/xen_drm_front.h
+   :doc: Driver limitations

Documentation/gpu/xen-zcopy.rst

@@ -0,0 +1,32 @@
+==============================================
+ drm/xen-zcopy Xen zero-copy helper DRM driver
+==============================================
+
+This helper driver allows implementing zero-copying use-cases
+when using Xen para-virtualized frontend display driver:
+
+ - a dumb buffer created on backend's side can be shared
+   with the Xen PV frontend driver, so it directly writes
+   into backend's domain memory (into the buffer exported from
+   DRM/KMS driver of a physical display device)
+ - a dumb buffer allocated by the frontend can be imported
+   into physical device DRM/KMS driver, thus allowing to
+   achieve no copying as well
+
+DRM_XEN_ZCOPY_DUMB_FROM_REFS IOCTL
+==================================
+
+.. kernel-doc:: include/uapi/drm/xen_zcopy_drm.h
+   :doc: DRM_XEN_ZCOPY_DUMB_FROM_REFS
+
+DRM_XEN_ZCOPY_DUMB_TO_REFS IOCTL
+================================
+
+.. kernel-doc:: include/uapi/drm/xen_zcopy_drm.h
+   :doc: DRM_XEN_ZCOPY_DUMB_TO_REFS
+
+DRM_XEN_ZCOPY_DUMB_WAIT_FREE IOCTL
+==================================
+
+.. kernel-doc:: include/uapi/drm/xen_zcopy_drm.h
+   :doc: DRM_XEN_ZCOPY_DUMB_WAIT_FREE

drivers/amba/bus.c

@@ -195,6 +195,7 @@ struct bus_type amba_bustype = {
 	.match		= amba_match,
 	.uevent		= amba_uevent,
 	.pm		= &amba_pm,
+	.force_dma	= true,
 };
 
 static int __init amba_init(void)

drivers/base/platform.c

@@ -1143,6 +1143,7 @@ struct bus_type platform_bus_type = {
 	.match		= platform_match,
 	.uevent		= platform_uevent,
 	.pm		= &platform_dev_pm_ops,
+	.force_dma	= true,
 };
 EXPORT_SYMBOL_GPL(platform_bus_type);
 

drivers/gpu/drm/Kconfig

@@ -278,6 +278,8 @@ source "drivers/gpu/drm/tinydrm/Kconfig"
 
 source "drivers/gpu/drm/pl111/Kconfig"
 
+source "drivers/gpu/drm/xen/Kconfig"
+
 # Keep legacy drivers last
 
 menuconfig DRM_LEGACY

drivers/gpu/drm/Makefile

@@ -101,3 +101,4 @@ obj-$(CONFIG_DRM_ZTE)	+= zte/
 obj-$(CONFIG_DRM_MXSFB)	+= mxsfb/
 obj-$(CONFIG_DRM_TINYDRM) += tinydrm/
 obj-$(CONFIG_DRM_PL111) += pl111/
+obj-$(CONFIG_DRM_XEN) += xen/

drivers/gpu/drm/drm_drv.c

@@ -32,6 +32,7 @@
 #include <linux/moduleparam.h>
 #include <linux/mount.h>
 #include <linux/slab.h>
+#include <linux/srcu.h>
 
 #include <drm/drm_drv.h>
 #include <drm/drmP.h>
@@ -74,6 +75,8 @@ static bool drm_core_init_complete = false;
 
 static struct dentry *drm_debugfs_root;
 
+DEFINE_STATIC_SRCU(drm_unplug_srcu);
+
 #define DRM_PRINTK_FMT "[" DRM_NAME ":%s]%s %pV"
 
 void drm_dev_printk(const struct device *dev, const char *level,
@@ -364,18 +367,51 @@ void drm_put_dev(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_put_dev);
 
-static void drm_device_set_unplugged(struct drm_device *dev)
+/**
+ * drm_dev_enter - Enter device critical section
+ * @dev: DRM device
+ * @idx: Pointer to index that will be passed to the matching drm_dev_exit()
+ *
+ * This function marks and protects the beginning of a section that should not
+ * be entered after the device has been unplugged. The section end is marked
+ * with drm_dev_exit(). Calls to this function can be nested.
+ *
+ * Returns:
+ * True if it is OK to enter the section, false otherwise.
+ */
+bool drm_dev_enter(struct drm_device *dev, int *idx)
+{
+	*idx = srcu_read_lock(&drm_unplug_srcu);
+
+	if (dev->unplugged) {
+		srcu_read_unlock(&drm_unplug_srcu, *idx);
+		return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(drm_dev_enter);
+
+/**
+ * drm_dev_exit - Exit device critical section
+ * @idx: index returned from drm_dev_enter()
+ *
+ * This function marks the end of a section that should not be entered after
+ * the device has been unplugged.
+ */
+void drm_dev_exit(int idx)
 {
-	smp_wmb();
-	atomic_set(&dev->unplugged, 1);
+	srcu_read_unlock(&drm_unplug_srcu, idx);
 }
+EXPORT_SYMBOL(drm_dev_exit);
 
 /**
  * drm_dev_unplug - unplug a DRM device
  * @dev: DRM device
  *
  * This unplugs a hotpluggable DRM device, which makes it inaccessible to
- * userspace operations. Entry-points can use drm_dev_is_unplugged(). This
+ * userspace operations. Entry-points can use drm_dev_enter() and
+ * drm_dev_exit() to protect device resources in a race free manner. This
  * essentially unregisters the device like drm_dev_unregister(), but can be
  * called while there are still open users of @dev.
  */
@@ -384,10 +420,18 @@ void drm_dev_unplug(struct drm_device *dev)
 	drm_dev_unregister(dev);
 
 	mutex_lock(&drm_global_mutex);
-	drm_device_set_unplugged(dev);
 	if (dev->open_count == 0)
 		drm_dev_unref(dev);
 	mutex_unlock(&drm_global_mutex);
+
+	/*
+	 * After synchronizing any critical read section is guaranteed to see
+	 * the new value of ->unplugged, and any critical section which might
+	 * still have seen the old value of ->unplugged is guaranteed to have
+	 * finished.
+	 */
+	dev->unplugged = true;
+	synchronize_srcu(&drm_unplug_srcu);
 }
 EXPORT_SYMBOL(drm_dev_unplug);
 

drivers/gpu/drm/drm_simple_kms_helper.c

@@ -34,6 +34,20 @@ static const struct drm_encoder_funcs drm_simple_kms_encoder_funcs = {
 	.destroy = drm_encoder_cleanup,
 };
 
+static enum drm_mode_status
+drm_simple_kms_crtc_mode_valid(struct drm_crtc *crtc,
+			       const struct drm_display_mode *mode)
+{
+	struct drm_simple_display_pipe *pipe;
+
+	pipe = container_of(crtc, struct drm_simple_display_pipe, crtc);
+	if (!pipe->funcs || !pipe->funcs->mode_valid)
+		/* Anything goes */
+		return MODE_OK;
+
+	return pipe->funcs->mode_valid(crtc, mode);
+}
+
 static int drm_simple_kms_crtc_check(struct drm_crtc *crtc,
 				     struct drm_crtc_state *state)
 {
@@ -50,13 +64,15 @@ static int drm_simple_kms_crtc_check(struct drm_crtc *crtc,
 static void drm_simple_kms_crtc_enable(struct drm_crtc *crtc,
 				       struct drm_crtc_state *old_state)
 {
+	struct drm_plane *plane;
 	struct drm_simple_display_pipe *pipe;
 
 	pipe = container_of(crtc, struct drm_simple_display_pipe, crtc);
 	if (!pipe->funcs || !pipe->funcs->enable)
 		return;
 
-	pipe->funcs->enable(pipe, crtc->state);
+	plane = &pipe->plane;
+	pipe->funcs->enable(pipe, crtc->state, plane->state);
 }
 
 static void drm_simple_kms_crtc_disable(struct drm_crtc *crtc,
@@ -72,6 +88,7 @@ static void drm_simple_kms_crtc_disable(struct drm_crtc *crtc,
 }
 
 static const struct drm_crtc_helper_funcs drm_simple_kms_crtc_helper_funcs = {
+	.mode_valid = drm_simple_kms_crtc_mode_valid,
 	.atomic_check = drm_simple_kms_crtc_check,
 	.atomic_enable = drm_simple_kms_crtc_enable,
 	.atomic_disable = drm_simple_kms_crtc_disable,
@@ -97,11 +114,11 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
 	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
 	crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
 						   &pipe->crtc);
-	if (!crtc_state->enable)
-		return 0; /* nothing to check when disabling or disabled */
 
-	clip.x2 = crtc_state->adjusted_mode.hdisplay;
-	clip.y2 = crtc_state->adjusted_mode.vdisplay;
+	if (crtc_state) {
+		clip.x2 = crtc_state->adjusted_mode.hdisplay;
+		clip.y2 = crtc_state->adjusted_mode.vdisplay;
+	}
 
 	ret = drm_plane_helper_check_state(plane_state, &clip,
 					   DRM_PLANE_HELPER_NO_SCALING,
@@ -111,7 +128,9 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
 		return ret;
 
 	if (!plane_state->visible)
-		return -EINVAL;
+		return 0;
+
+	drm_mode_get_hv_timing(&crtc_state->mode, &clip.x2, &clip.y2);
 
 	if (!pipe->funcs || !pipe->funcs->check)
 		return 0;

drivers/gpu/drm/mxsfb/mxsfb_drv.c

@@ -98,7 +98,8 @@ static const struct drm_mode_config_funcs mxsfb_mode_config_funcs = {
 };
 
 static void mxsfb_pipe_enable(struct drm_simple_display_pipe *pipe,
-			      struct drm_crtc_state *crtc_state)
+			      struct drm_crtc_state *crtc_state,
+			      struct drm_plane_state *plane_state)
 {
 	struct mxsfb_drm_private *mxsfb = drm_pipe_to_mxsfb_drm_private(pipe);
 

drivers/gpu/drm/pl111/pl111_display.c

@@ -86,7 +86,8 @@ static int pl111_display_check(struct drm_simple_display_pipe *pipe,
 }
 
 static void pl111_display_enable(struct drm_simple_display_pipe *pipe,
-				 struct drm_crtc_state *cstate)
+				 struct drm_crtc_state *cstate,
+				 struct drm_plane_state *plane_state)
 {
 	struct drm_crtc *crtc = &pipe->crtc;
 	struct drm_plane *plane = &pipe->plane;

drivers/gpu/drm/tinydrm/repaper.c

@@ -659,7 +659,8 @@ static void power_off(struct repaper_epd *epd)
 }
 
 static void repaper_pipe_enable(struct drm_simple_display_pipe *pipe,
-				struct drm_crtc_state *crtc_state)
+				struct drm_crtc_state *crtc_state,
+				struct drm_plane_state *plane_state)
 {
 	struct tinydrm_device *tdev = pipe_to_tinydrm(pipe);
 	struct repaper_epd *epd = epd_from_tinydrm(tdev);

drivers/gpu/drm/tinydrm/st7586.c

@@ -173,7 +173,8 @@ static const struct drm_framebuffer_funcs st7586_fb_funcs = {
 };
 
 static void st7586_pipe_enable(struct drm_simple_display_pipe *pipe,
-			       struct drm_crtc_state *crtc_state)
+			       struct drm_crtc_state *crtc_state,
+			       struct drm_plane_state *plane_state)
 {
 	struct tinydrm_device *tdev = pipe_to_tinydrm(pipe);
 	struct mipi_dbi *mipi = mipi_dbi_from_tinydrm(tdev);

drivers/gpu/drm/xen/Kconfig

@@ -0,0 +1,42 @@
+config DRM_XEN
+	bool "DRM Support for Xen guest OS"
+	depends on XEN
+	help
+	  Choose this option if you want to enable DRM support
+	  for Xen.
+
+choice
+	prompt "Xen DRM drivers selection"
+	depends on DRM_XEN
+
+config DRM_XEN_FRONTEND
+	tristate "Para-virtualized frontend driver for Xen guest OS"
+	depends on DRM_XEN
+	depends on DRM
+	select DRM_KMS_HELPER
+	select VIDEOMODE_HELPERS
+	select XEN_XENBUS_FRONTEND
+	help
+	  Choose this option if you want to enable a para-virtualized
+	  frontend DRM/KMS driver for Xen guest OSes.
+
+config DRM_XEN_ZCOPY
+	tristate "Zero copy helper DRM driver for Xen"
+	depends on DRM_XEN
+	depends on DRM
+	select DRM_KMS_HELPER
+	help
+	  Choose this option if you want to enable a zero copy
+	  helper DRM driver for Xen. This is implemented via mapping
+	  of foreign display buffer pages into current domain and
+	  exporting a dumb via PRIME interface. This allows
+	  driver domains to use buffers of unpriveledged guests without
+	  additional memory copying.
+
+config DRM_XEN_ZCOPY_CMA
+	bool "Use CMA to allocate buffers"
+	depends on DRM_XEN_ZCOPY
+	help
+	  Use CMA to allocate display buffers.
+
+endchoice

drivers/gpu/drm/xen/Makefile

@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0 OR MIT
+
+drm_xen_front-objs := xen_drm_front.o \
+		      xen_drm_front_kms.o \
+		      xen_drm_front_conn.o \
+		      xen_drm_front_evtchnl.o \
+		      xen_drm_front_shbuf.o \
+		      xen_drm_front_cfg.o \
+		      xen_drm_front_gem.o
+
+obj-$(CONFIG_DRM_XEN_FRONTEND) += drm_xen_front.o
+
+drm_xen_zcopy-objs := xen_drm_zcopy.o \
+		      xen_drm_zcopy_balloon.o
+
+obj-$(CONFIG_DRM_XEN_ZCOPY) += drm_xen_zcopy.o