[PATCH v2 01/64] dmaengine: add tasklet-backed channel BH helpers
From: Allen Pais
Date: Mon Jul 27 2026 - 16:31:13 EST
DMAengine drivers commonly use a per-channel tasklet to invoke client
callbacks. Add helpers that initialize, schedule, and kill a channel
bottom half, with an initial tasklet-backed implementation that preserves
the existing execution context.
Convert virt-dma to the new API and remove its private tasklet. While
touching the completion handler, avoid forming a result pointer from a
NULL cyclic descriptor.
This establishes a backend-independent API before changing how channel
bottom halves are dispatched.
Signed-off-by: Allen Pais <allen.lkml@xxxxxxxxx>
---
drivers/dma/dmaengine.c | 42 +++++++++++++++++++++++++++++++++++++++
drivers/dma/virt-dma.c | 12 +++++------
drivers/dma/virt-dma.h | 7 +++----
include/linux/dmaengine.h | 28 ++++++++++++++++++++++++++
4 files changed, 79 insertions(+), 10 deletions(-)
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 9049171df857..f43aeecb47f9 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -1428,6 +1428,48 @@ static void dmaengine_destroy_unmap_pool(void)
}
}
+static void dma_chan_bh_entry(struct tasklet_struct *tasklet)
+{
+ struct dma_chan *chan = from_tasklet(chan, tasklet, bh_tasklet);
+ dma_chan_bh_work_fn fn = READ_ONCE(chan->bh_work_fn);
+
+ if (fn)
+ fn(chan);
+}
+
+void dma_chan_init_bh(struct dma_chan *chan, dma_chan_bh_work_fn fn)
+{
+ if (WARN_ON(!fn))
+ return;
+
+ if (WARN_ON(chan->bh_work_initialized))
+ return;
+
+ chan->bh_work_fn = fn;
+ tasklet_setup(&chan->bh_tasklet, dma_chan_bh_entry);
+ chan->bh_work_initialized = true;
+}
+EXPORT_SYMBOL_GPL(dma_chan_init_bh);
+
+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;
+}
+EXPORT_SYMBOL_GPL(dma_chan_schedule_bh);
+
+void dma_chan_kill_bh(struct dma_chan *chan)
+{
+ if (!chan->bh_work_initialized)
+ return;
+
+ tasklet_kill(&chan->bh_tasklet);
+}
+EXPORT_SYMBOL_GPL(dma_chan_kill_bh);
+
static int __init dmaengine_init_unmap_pool(void)
{
int i;
diff --git a/drivers/dma/virt-dma.c b/drivers/dma/virt-dma.c
index 7961172a780d..89fcd51ddcab 100644
--- a/drivers/dma/virt-dma.c
+++ b/drivers/dma/virt-dma.c
@@ -77,12 +77,12 @@ struct virt_dma_desc *vchan_find_desc(struct virt_dma_chan *vc,
EXPORT_SYMBOL_GPL(vchan_find_desc);
/*
- * This tasklet handles the completion of a DMA descriptor by
- * calling its callback and freeing it.
+ * This bottom-half handler completes a DMA descriptor by invoking its
+ * callback and freeing it.
*/
-static void vchan_complete(struct tasklet_struct *t)
+static void vchan_complete(struct dma_chan *chan)
{
- struct virt_dma_chan *vc = from_tasklet(vc, t, task);
+ struct virt_dma_chan *vc = to_virt_chan(chan);
struct virt_dma_desc *vd, *_vd;
struct dmaengine_desc_callback cb;
LIST_HEAD(head);
@@ -98,7 +98,7 @@ static void vchan_complete(struct tasklet_struct *t)
}
spin_unlock_irq(&vc->lock);
- dmaengine_desc_callback_invoke(&cb, &vd->tx_result);
+ dmaengine_desc_callback_invoke(&cb, vd ? &vd->tx_result : NULL);
list_for_each_entry_safe(vd, _vd, &head, node) {
dmaengine_desc_get_callback(&vd->tx, &cb);
@@ -131,7 +131,7 @@ void vchan_init(struct virt_dma_chan *vc, struct dma_device *dmadev)
INIT_LIST_HEAD(&vc->desc_completed);
INIT_LIST_HEAD(&vc->desc_terminated);
- tasklet_setup(&vc->task, vchan_complete);
+ dma_chan_init_bh(&vc->chan, vchan_complete);
vc->chan.device = dmadev;
list_add_tail(&vc->chan.device_node, &dmadev->channels);
diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h
index 59d9eabc8b67..abe2a4475744 100644
--- a/drivers/dma/virt-dma.h
+++ b/drivers/dma/virt-dma.h
@@ -21,7 +21,6 @@ struct virt_dma_desc {
struct virt_dma_chan {
struct dma_chan chan;
- struct tasklet_struct task;
void (*desc_free)(struct virt_dma_desc *);
spinlock_t lock;
@@ -106,7 +105,7 @@ static inline void vchan_cookie_complete(struct virt_dma_desc *vd)
vd, cookie);
list_add_tail(&vd->node, &vc->desc_completed);
- tasklet_schedule(&vc->task);
+ dma_chan_schedule_bh(&vc->chan);
}
/**
@@ -137,7 +136,7 @@ static inline void vchan_cyclic_callback(struct virt_dma_desc *vd)
struct virt_dma_chan *vc = to_virt_chan(vd->tx.chan);
vc->cyclic = vd;
- tasklet_schedule(&vc->task);
+ dma_chan_schedule_bh(&vc->chan);
}
/**
@@ -223,7 +222,7 @@ static inline void vchan_synchronize(struct virt_dma_chan *vc)
LIST_HEAD(head);
unsigned long flags;
- tasklet_kill(&vc->task);
+ dma_chan_kill_bh(&vc->chan);
spin_lock_irqsave(&vc->lock, flags);
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index b3d251c9734e..c670781b3150 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -12,6 +12,7 @@
#include <linux/scatterlist.h>
#include <linux/bitmap.h>
#include <linux/types.h>
+#include <linux/interrupt.h>
#include <asm/page.h>
/**
@@ -295,6 +296,10 @@ enum dma_desc_metadata_mode {
DESC_METADATA_ENGINE = BIT(1),
};
+struct dma_chan;
+
+typedef void (*dma_chan_bh_work_fn)(struct dma_chan *chan);
+
/**
* struct dma_chan_percpu - the per-CPU part of struct dma_chan
* @memcpy_count: transaction counter
@@ -334,6 +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
*/
struct dma_chan {
struct dma_device *device;
@@ -359,6 +367,9 @@ struct dma_chan {
void *route_data;
void *private;
+ struct tasklet_struct bh_tasklet;
+ dma_chan_bh_work_fn bh_work_fn;
+ bool bh_work_initialized;
};
/**
@@ -1529,6 +1540,9 @@ struct dma_chan *devm_dma_request_chan(struct device *dev, const char *name);
void dma_release_channel(struct dma_chan *chan);
int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps);
+void dma_chan_init_bh(struct dma_chan *chan, dma_chan_bh_work_fn fn);
+bool dma_chan_schedule_bh(struct dma_chan *chan);
+void dma_chan_kill_bh(struct dma_chan *chan);
#else
static inline struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type)
{
@@ -1576,6 +1590,20 @@ static inline int dma_get_slave_caps(struct dma_chan *chan,
{
return -ENXIO;
}
+
+static inline void dma_chan_init_bh(struct dma_chan *chan,
+ dma_chan_bh_work_fn fn)
+{
+}
+
+static inline bool dma_chan_schedule_bh(struct dma_chan *chan)
+{
+ return false;
+}
+
+static inline void dma_chan_kill_bh(struct dma_chan *chan)
+{
+}
#endif
static inline int dmaengine_desc_set_reuse(struct dma_async_tx_descriptor *tx)
--
2.43.0