[RFC PATCH v4 04/38] dmaengine: dw-edma: Add notify-only channels support

Koichiro Den
2026-01-18T13:55:06Z

Remote eDMA users may want to prepare descriptors on the remote side while
the local side only needs completion notifications (no cookie-based
accounting).

Provide a lightweight per-channel notification callback infrastructure.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
drivers/dma/dw-edma/dw-edma-core.c | 31 ++++++++++++++++++++++++++++++
drivers/dma/dw-edma/dw-edma-core.h | 4 ++++
include/linux/dma/edma.h | 23 ++++++++++++++++++++++
3 files changed, 58 insertions(+)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index 696b9f3ea378..0eb8fc1dcc34 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -611,6 +611,13 @@ static void dw_edma_done_interrupt(struct dw_edma_chan *chan)
struct virt_dma_desc *vd;
unsigned long flags;

+ if (chan->notify_only) {
+ if (chan->notify_cb)
+ chan->notify_cb(&chan->vc.chan, chan->notify_cb_param);
+ /* no cookie on this side, just return */
+ return;
+ }
+
spin_lock_irqsave(&chan->vc.lock, flags);
vd = vchan_next_desc(&chan->vc);
if (vd) {
@@ -815,6 +822,9 @@ static int dw_edma_channel_setup(struct dw_edma *dw, u32 wr_alloc, u32 rd_alloc)
chan->request = EDMA_REQ_NONE;
chan->status = EDMA_ST_IDLE;
chan->irq_mode = DW_EDMA_CH_IRQ_DEFAULT;
+ chan->notify_cb = NULL;
+ chan->notify_cb_param = NULL;
+ chan->notify_only = false;

if (chan->dir == EDMA_DIR_WRITE)
chan->ll_max = (chip->ll_region_wr[chan->id].sz / EDMA_LL_SZ);
@@ -1178,6 +1188,27 @@ bool dw_edma_chan_ignore_irq(struct dma_chan *dchan)
}
EXPORT_SYMBOL_GPL(dw_edma_chan_ignore_irq);

+int dw_edma_chan_register_notify(struct dma_chan *dchan,
+ void (*cb)(struct dma_chan *chan, void *user),
+ void *user)
+{
+ struct dw_edma_chan *chan;
+
+ if (!dchan || !dchan->device)
+ return -ENODEV;
+
+ chan = dchan2dw_edma_chan(dchan);
+ if (!chan)
+ return -ENODEV;
+
+ chan->notify_cb = cb;
+ chan->notify_cb_param = user;
+ chan->notify_only = !!cb;
+
+ return dw_edma_chan_irq_config(dchan, DW_EDMA_CH_IRQ_LOCAL);
+}
+EXPORT_SYMBOL_GPL(dw_edma_chan_register_notify);
+
MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Synopsys DesignWare eDMA controller core driver");
MODULE_AUTHOR("Gustavo Pimentel <gustavo.pimentel@synopsys.com>");
diff --git a/drivers/dma/dw-edma/dw-edma-core.h b/drivers/dma/dw-edma/dw-edma-core.h
index 11fe4532f0bf..f652d2e38843 100644
--- a/drivers/dma/dw-edma/dw-edma-core.h
+++ b/drivers/dma/dw-edma/dw-edma-core.h
@@ -84,6 +84,10 @@ struct dw_edma_chan {

enum dw_edma_ch_irq_mode irq_mode;

+ void (*notify_cb)(struct dma_chan *chan, void *user);
+ void *notify_cb_param;
+ bool notify_only;
+
struct delayed_work poll_work;
spinlock_t poll_lock;

diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
index 6f50165ac084..3c538246de07 100644
--- a/include/linux/dma/edma.h
+++ b/include/linux/dma/edma.h
@@ -138,6 +138,21 @@ int dw_edma_chan_irq_config(struct dma_chan *chan,
* @chan: DMA channel obtained from dma_request_channel()
*/
bool dw_edma_chan_ignore_irq(struct dma_chan *chan);
+
+/**
+ * dw_edma_chan_register_notify - register local completion callback for a
+ * notification-only channel
+ * @chan: DMA channel obtained from dma_request_channel()
+ * @cb: callback invoked in hardirq context when LIE interrupt is raised
+ * @user: opaque pointer passed back to @cb
+ *
+ * Intended for channels where descriptors are prepared on the remote side and
+ * the local side only wants completion notifications. This forces LOCAL mode
+ * so that the local side receives LIE interrupts.
+ */
+int dw_edma_chan_register_notify(struct dma_chan *chan,
+ void (*cb)(struct dma_chan *chan, void *user),
+ void *user);
#else
static inline int dw_edma_probe(struct dw_edma_chip *chip)
{
@@ -159,6 +174,14 @@ static inline bool dw_edma_chan_ignore_irq(struct dma_chan *chan)
{
return false;
}
+
+static inline int dw_edma_chan_register_notify(struct dma_chan *chan,
+ void (*cb)(struct dma_chan *chan,
+ void *user),
+ void *user)
+{
+ return -ENODEV;
+}
#endif /* CONFIG_DW_EDMA */

struct pci_epc;
--
2.51.0