[RFC PATCH v3 12/21] dma-buf/dma-resv: Introduce dma_resv_trylock_ctx()

[Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>]

For the drm_exec_trylock() functionality, there is a need to be able
to trylock a dma-resv object as part of a drm_exec transaction.
Therefore expose a variant of dma_resv_trylock that also takes
a struct ww_acquire_ctx parameter.

Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Somalapuram Amaranath <Amaranath.Somalapuram@xxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
Cc: <linaro-mm-sig@xxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
 include/linux/dma-resv.h | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index 8d0e34dad446..68dae8f2a22c 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -405,6 +405,27 @@ static inline int dma_resv_lock_slow_interruptible(struct dma_resv *obj,
 	return ww_mutex_lock_slow_interruptible(&obj->lock, ctx);
 }
 
+/**
+ * dma_resv_trylock_ctx - trylock the reservation object
+ * @obj: the reservation object
+ * @ctx: The ww acquire context or NULL.
+ *
+ * Tries to lock the reservation object for exclusive access and modification.
+ * Note, that the lock is only against other writers, readers will run
+ * concurrently with a writer under RCU. The seqlock is used to notify readers
+ * if they overlap with a writer. The context parameter ensures that other
+ * ww transactions can perform deadlock backoff if necessary, and that
+ * subsequent attempts to dma_resv_lock() @obj for @ctx will return
+ * -EALREADY.
+ *
+ * Return: true if the lock was acquired, false otherwise.
+ */
+static inline bool __must_check
+dma_resv_trylock_ctx(struct dma_resv *obj, struct ww_acquire_ctx *ctx)
+{
+	return ww_mutex_trylock(&obj->lock, ctx);
+}
+
 /**
  * dma_resv_trylock - trylock the reservation object
  * @obj: the reservation object
@@ -421,7 +442,7 @@ static inline int dma_resv_lock_slow_interruptible(struct dma_resv *obj,
  */
 static inline bool __must_check dma_resv_trylock(struct dma_resv *obj)
 {
-	return ww_mutex_trylock(&obj->lock, NULL);
+	return dma_resv_trylock_ctx(obj, NULL);
 }
 
 /**
-- 
2.44.0