[Intel-gfx] [PATCH 01/28] drm/i915: Fix i915_request fence wait semantics

Maarten Lankhorst
2021-10-21T10:36:51Z

The i915_request fence wait behaves differently for timeout = 0
compared to expected dma-fence behavior.

i915 behavior:
- Unsignaled: -ETIME
- Signaled: 0 (= timeout)

Expected:
- Unsignaled: 0
- Signaled: 1

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
drivers/gpu/drm/i915/i915_request.c | 57 ++++++++++++++++++++++++-----
drivers/gpu/drm/i915/i915_request.h | 5 +++
2 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 820a1f38b271..42cd17357771 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -96,9 +96,9 @@ static signed long i915_fence_wait(struct dma_fence *fence,
bool interruptible,
signed long timeout)
{
- return i915_request_wait(to_request(fence),
- interruptible | I915_WAIT_PRIORITY,
- timeout);
+ return i915_request_wait_timeout(to_request(fence),
+ interruptible | I915_WAIT_PRIORITY,
+ timeout);
}

struct kmem_cache *i915_request_slab_cache(void)
@@ -1857,23 +1857,27 @@ static void request_wait_wake(struct dma_fence *fence, struct dma_fence_cb *cb)
}

/**
- * i915_request_wait - wait until execution of request has finished
+ * i915_request_wait_timeout - wait until execution of request has finished
* @rq: the request to wait upon
* @flags: how to wait
* @timeout: how long to wait in jiffies
*
- * i915_request_wait() waits for the request to be completed, for a
+ * i915_request_wait_timeout() waits for the request to be completed, for a
* maximum of @timeout jiffies (with MAX_SCHEDULE_TIMEOUT implying an
* unbounded wait).
*
* Returns the remaining time (in jiffies) if the request completed, which may
- * be zero or -ETIME if the request is unfinished after the timeout expires.
+ * be zero if the request is unfinished after the timeout expires.
+ * If the timeout is 0, it will return 1 if the fence is signaled.
+ *
* May return -EINTR is called with I915_WAIT_INTERRUPTIBLE and a signal is
* pending before the request completes.
+ *
+ * NOTE: This function has the same wait semantics as dma-fence.
*/
-long i915_request_wait(struct i915_request *rq,
- unsigned int flags,
- long timeout)
+long i915_request_wait_timeout(struct i915_request *rq,
+ unsigned int flags,
+ long timeout)
{
const int state = flags & I915_WAIT_INTERRUPTIBLE ?
TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
@@ -1883,7 +1887,7 @@ long i915_request_wait(struct i915_request *rq,
GEM_BUG_ON(timeout < 0);

if (dma_fence_is_signaled(&rq->fence))
- return timeout;
+ return timeout ?: 1;

if (!timeout)
return -ETIME;
@@ -1992,6 +1996,39 @@ long i915_request_wait(struct i915_request *rq,
return timeout;
}

+/**
+ * i915_request_wait - wait until execution of request has finished
+ * @rq: the request to wait upon
+ * @flags: how to wait
+ * @timeout: how long to wait in jiffies
+ *
+ * i915_request_wait() waits for the request to be completed, for a
+ * maximum of @timeout jiffies (with MAX_SCHEDULE_TIMEOUT implying an
+ * unbounded wait).
+ *
+ * Returns the remaining time (in jiffies) if the request completed, which may
+ * be zero or -ETIME if the request is unfinished after the timeout expires.
+ * May return -EINTR is called with I915_WAIT_INTERRUPTIBLE and a signal is
+ * pending before the request completes.
+ *
+ * NOTE: This function behaves differently from dma-fence wait semantics for
+ * timeout = 0. It returns 0 on success, and -ETIME if not signaled.
+ */
+long i915_request_wait(struct i915_request *rq,
+ unsigned int flags,
+ long timeout)
+{
+ long ret = i915_request_wait_timeout(rq, flags, timeout);
+
+ if (!ret)
+ return -ETIME;
+
+ if (ret > 0 && !timeout)
+ return 0;
+
+ return ret;
+}
+
static int print_sched_attr(const struct i915_sched_attr *attr,
char *buf, int x, int len)
{
diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index dc359242d1ae..3c6e8acd1457 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -414,6 +414,11 @@ void i915_request_unsubmit(struct i915_request *request);

void i915_request_cancel(struct i915_request *rq, int error);

+long i915_request_wait_timeout(struct i915_request *rq,
+ unsigned int flags,
+ long timeout)
+ __attribute__((nonnull(1)));
+
long i915_request_wait(struct i915_request *rq,
unsigned int flags,
long timeout)
--
2.33.0