linux-kernel - [RFC PATCH v3 20/35] dmaengine: dw-edma: Add notify-only channels support

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Message-ID: <20251217151609.3162665-21-den@valinux.co.jp>
Date: Thu, 18 Dec 2025 00:15:54 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Frank.Li@....com,
	dave.jiang@...el.com,
	ntb@...ts.linux.dev,
	linux-pci@...r.kernel.org,
	dmaengine@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
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Subject: [RFC PATCH v3 20/35] dmaengine: dw-edma: Add notify-only channels support

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@...inux.co.jp>
---
 drivers/dma/dw-edma/dw-edma-core.c | 32 ++++++++++++++++++++++++++++++
 drivers/dma/dw-edma/dw-edma-core.h |  4 ++++
 include/linux/dma/edma.h           | 22 ++++++++++++++++++++
 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 09b10ad1f38a..8e262f61f02d 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -608,6 +608,13 @@ 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) {
@@ -811,6 +818,9 @@ 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);
@@ -1171,6 +1181,28 @@ 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 ||
+	    dchan->device->device_prep_slave_sg_config != dw_edma_device_prep_slave_sg_config)
+		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@...opsys.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 8c1b1d25fa44..4caf5cc5c368 100644
--- a/include/linux/dma/edma.h
+++ b/include/linux/dma/edma.h
@@ -95,6 +95,21 @@ int dw_edma_chan_irq_config(struct dma_chan *chan,
  */
 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);
+
 #if IS_REACHABLE(CONFIG_PCIE_DW)
 /**
  * dw_edma_get_reg_window - get eDMA register base and size
@@ -185,6 +200,13 @@ 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
 
 #endif /* _DW_EDMA_H */
-- 
2.51.0