[PATCH v2 02/64] dmaengine: back channel BH helpers with WQ_BH

[Allen Pais]

Replace the tasklet implementation of the channel BH helpers with a
dedicated WQ_BH | WQ_PERCPU workqueue. The public dma_chan_*_bh() API and
its softirq execution context remain unchanged.

Keep the workqueue operations internal to dmaengine. Drain scheduled work
in dma_chan_kill_bh() to preserve the completion semantics of
tasklet_kill().

Signed-off-by: Allen Pais <allen.lkml@xxxxxxxxx>
---
 drivers/dma/dmaengine.c   | 59 ++++++++++++++++++++++++++++++++-------
 include/linux/dmaengine.h | 10 +++----
 2 files changed, 54 insertions(+), 15 deletions(-)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index f43aeecb47f9..8b1b17794956 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -54,6 +54,7 @@
 #include <linux/rcupdate.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/workqueue.h>
 
 #include "dmaengine.h"
 
@@ -61,6 +62,7 @@ static DEFINE_MUTEX(dma_list_mutex);
 static DEFINE_IDA(dma_ida);
 static LIST_HEAD(dma_device_list);
 static long dmaengine_ref_count;
+static struct workqueue_struct *dmaengine_bh_wq;
 
 /* --- debugfs implementation --- */
 #ifdef CONFIG_DEBUG_FS
@@ -1428,9 +1430,34 @@ static void dmaengine_destroy_unmap_pool(void)
 	}
 }
 
-static void dma_chan_bh_entry(struct tasklet_struct *tasklet)
+static void dmaengine_destroy_bh_wq(void)
 {
-	struct dma_chan *chan = from_tasklet(chan, tasklet, bh_tasklet);
+	if (!dmaengine_bh_wq)
+		return;
+
+	destroy_workqueue(dmaengine_bh_wq);
+	dmaengine_bh_wq = NULL;
+}
+
+static bool dmaengine_queue_bh_work(struct work_struct *work)
+{
+	if (WARN_ON(!dmaengine_bh_wq))
+		return false;
+
+	return queue_work(dmaengine_bh_wq, work);
+}
+
+static void dmaengine_flush_bh_work(struct work_struct *work)
+{
+	if (!work)
+		return;
+
+	flush_work(work);
+}
+
+static void dma_chan_bh_entry(struct work_struct *work)
+{
+	struct dma_chan *chan = container_of(work, struct dma_chan, bh_work);
 	dma_chan_bh_work_fn fn = READ_ONCE(chan->bh_work_fn);
 
 	if (fn)
@@ -1446,7 +1473,7 @@ void dma_chan_init_bh(struct dma_chan *chan, dma_chan_bh_work_fn fn)
 		return;
 
 	chan->bh_work_fn = fn;
-	tasklet_setup(&chan->bh_tasklet, dma_chan_bh_entry);
+	INIT_WORK(&chan->bh_work, dma_chan_bh_entry);
 	chan->bh_work_initialized = true;
 }
 EXPORT_SYMBOL_GPL(dma_chan_init_bh);
@@ -1456,8 +1483,7 @@ bool dma_chan_schedule_bh(struct dma_chan *chan)
 	if (WARN_ON(!chan->bh_work_initialized))
 		return false;
 
-	tasklet_schedule(&chan->bh_tasklet);
-	return true;
+	return dmaengine_queue_bh_work(&chan->bh_work);
 }
 EXPORT_SYMBOL_GPL(dma_chan_schedule_bh);
 
@@ -1466,7 +1492,7 @@ void dma_chan_kill_bh(struct dma_chan *chan)
 	if (!chan->bh_work_initialized)
 		return;
 
-	tasklet_kill(&chan->bh_tasklet);
+	dmaengine_flush_bh_work(&chan->bh_work);
 }
 EXPORT_SYMBOL_GPL(dma_chan_kill_bh);
 
@@ -1666,15 +1692,28 @@ EXPORT_SYMBOL_GPL(dma_run_dependencies);
 
 static int __init dma_bus_init(void)
 {
-	int err = dmaengine_init_unmap_pool();
+	int err;
 
+	dmaengine_bh_wq = alloc_workqueue("dmaengine_bh",
+					  WQ_BH | WQ_PERCPU, 0);
+	if (!dmaengine_bh_wq)
+		return -ENOMEM;
+
+	err = dmaengine_init_unmap_pool();
 	if (err)
-		return err;
+		goto err_destroy_wq;
 
 	err = class_register(&dma_devclass);
-	if (!err)
-		dmaengine_debugfs_init();
+	if (err)
+		goto err_destroy_pool;
 
+	dmaengine_debugfs_init();
+	return 0;
+
+err_destroy_pool:
+	dmaengine_destroy_unmap_pool();
+err_destroy_wq:
+	dmaengine_destroy_bh_wq();
 	return err;
 }
 arch_initcall(dma_bus_init);
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index c670781b3150..c87974d5048b 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -12,7 +12,7 @@
 #include <linux/scatterlist.h>
 #include <linux/bitmap.h>
 #include <linux/types.h>
-#include <linux/interrupt.h>
+#include <linux/workqueue.h>
 #include <asm/page.h>
 
 /**
@@ -339,9 +339,9 @@ struct dma_router {
  * @router: pointer to the DMA router structure
  * @route_data: channel specific data for the router
  * @private: private data for certain client-channel associations
- * @bh_tasklet: bottom-half tasklet stored per-channel
- * @bh_work_fn: callback executed when @bh_tasklet runs
- * @bh_work_initialized: indicates whether @bh_tasklet has been initialized
+ * @bh_work: bottom-half work item stored per-channel
+ * @bh_work_fn: callback executed when @bh_work runs
+ * @bh_work_initialized: indicates whether @bh_work has been initialized
  */
 struct dma_chan {
 	struct dma_device *device;
@@ -367,7 +367,7 @@ struct dma_chan {
 	void *route_data;
 
 	void *private;
-	struct tasklet_struct bh_tasklet;
+	struct work_struct bh_work;
 	dma_chan_bh_work_fn bh_work_fn;
 	bool bh_work_initialized;
 };
-- 
2.43.0