[Intel-xe] [PATCH v3] drm/xe: Use nanoseconds instead of jiffies in uapi for user fence

[Zbigniew Kempczyński]

Using jiffies as a timeout from userspace is weird even it theoretically
exists possiblity of acquiring jiffies via getconf. Unfortunately this
method is unreliable and returned value may vary from configured in the
kernel config.

>From now on timeout is expressed in nanoseconds and its interpretation
depends on setting DRM_XE_UFENCE_WAIT_ABSTIME flag. Relative timeout
(flag is not set) means fence expire at now() + timeout. Absolute
timeout (flag is set) means fence will expire at exact point of time.

Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
Cc: Andi Shyti <andi.shyti at linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com>
---
 drivers/gpu/drm/xe/xe_wait_user_fence.c | 40 ++++++++++++++++++-------
 include/uapi/drm/xe_drm.h               | 14 ++++++++-
 2 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_wait_user_fence.c b/drivers/gpu/drm/xe/xe_wait_user_fence.c
index 6c8a60c60087..4405e694fe21 100644
--- a/drivers/gpu/drm/xe/xe_wait_user_fence.c
+++ b/drivers/gpu/drm/xe/xe_wait_user_fence.c
@@ -7,6 +7,7 @@
 
 #include <drm/drm_device.h>
 #include <drm/drm_file.h>
+#include <drm/drm_utils.h>
 #include <drm/xe_drm.h>
 
 #include "xe_device.h"
@@ -84,6 +85,24 @@ static int check_hw_engines(struct xe_device *xe,
 			 DRM_XE_UFENCE_WAIT_VM_ERROR)
 #define MAX_OP		DRM_XE_UFENCE_WAIT_LTE
 
+static unsigned long to_jiffies_timeout(struct drm_xe_wait_user_fence *args)
+{
+	unsigned long timeout;
+
+	if (args->flags & DRM_XE_UFENCE_WAIT_ABSTIME)
+		return drm_timeout_abs_to_jiffies(args->timeout);
+
+	if (args->timeout < 0)
+		return MAX_SCHEDULE_TIMEOUT;
+
+	if (args->timeout == 0)
+		return 0;
+
+	timeout = nsecs_to_jiffies(args->timeout);
+
+	return timeout ?: 1;
+}
+
 int xe_wait_user_fence_ioctl(struct drm_device *dev, void *data,
 			     struct drm_file *file)
 {
@@ -98,7 +117,8 @@ int xe_wait_user_fence_ioctl(struct drm_device *dev, void *data,
 	int err;
 	bool no_engines = args->flags & DRM_XE_UFENCE_WAIT_SOFT_OP ||
 		args->flags & DRM_XE_UFENCE_WAIT_VM_ERROR;
-	unsigned long timeout = args->timeout;
+	unsigned long timeout;
+	ktime_t start;
 
 	if (XE_IOCTL_ERR(xe, args->extensions) || XE_IOCTL_ERR(xe, args->pad) ||
 	    XE_IOCTL_ERR(xe, args->reserved[0] || args->reserved[1]))
@@ -149,8 +169,8 @@ int xe_wait_user_fence_ioctl(struct drm_device *dev, void *data,
 		addr = vm->async_ops.error_capture.addr;
 	}
 
-	if (XE_IOCTL_ERR(xe, timeout > MAX_SCHEDULE_TIMEOUT))
-		return -EINVAL;
+	timeout = to_jiffies_timeout(args);
+	start = ktime_get();
 
 	/*
 	 * FIXME: Very simple implementation at the moment, single wait queue
@@ -189,17 +209,17 @@ int xe_wait_user_fence_ioctl(struct drm_device *dev, void *data,
 	} else {
 		remove_wait_queue(&xe->ufence_wq, &w_wait);
 	}
+
+	if (!(args->flags & DRM_XE_UFENCE_WAIT_ABSTIME)) {
+		args->timeout -= ktime_to_ns(ktime_sub(ktime_get(), start));
+		if (args->timeout < 0)
+			args->timeout = 0;
+	}
+
 	if (XE_IOCTL_ERR(xe, err < 0))
 		return err;
 	else if (XE_IOCTL_ERR(xe, !timeout))
 		return -ETIME;
 
-	/*
-	 * Again very simple, return the time in jiffies that has past, may need
-	 * a more precision
-	 */
-	if (args->flags & DRM_XE_UFENCE_WAIT_ABSTIME)
-		args->timeout = args->timeout - timeout;
-
 	return 0;
 }
diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
index 7f9a5849e88b..0a1256e76f38 100644
--- a/include/uapi/drm/xe_drm.h
+++ b/include/uapi/drm/xe_drm.h
@@ -732,7 +732,19 @@ struct drm_xe_wait_user_fence {
 #define DRM_XE_UFENCE_WAIT_U32		0xffffffffu
 #define DRM_XE_UFENCE_WAIT_U64		0xffffffffffffffffu
 	__u64 mask;
-	/** @timeout: how long to wait before bailing, value in jiffies */
+	/**
+	 * @timeout: how long to wait before bailing, value in nanoseconds.
+	 * Without DRM_XE_UFENCE_WAIT_ABSTIME flag set (relative timeout)
+	 * it contains timeout expressed in nanoseconds to wait (fence will
+	 * expire at now() + timeout).
+	 * When DRM_XE_UFENCE_WAIT_ABSTIME flat is set (absolute timeout) wait
+	 * will end at timeout (uses system MONOTONIC_CLOCK).
+	 *
+	 * On relative timeout this value is updated with timeout left
+	 * (for restarting the call in case of signal delivery).
+	 * On absolute timeout this value stays intact (restarted call still
+	 * expire at the same point of time).
+	 */
 	__s64 timeout;
 	/**
 	 * @num_engines: number of engine instances to wait on, must be zero
-- 
2.34.1