[PATCH v7 05/10] dmaengine: dw-edma: Add channel delegation helpers

[Koichiro Den]

Endpoint functions that expose endpoint-local DesignWare eDMA channels
to a remote host need to reserve exact hardware channels and hand
interrupt ownership to the remote side before publishing the channels.

Add DW eDMA-specific helpers that validate an idle, already reserved
channel and switch it to remote interrupt routing. The matching reclaim
helper can quiesce the channel while it is still remote-routed, then
restores the channel's default routing. The dmaengine channel reservation
remains with the caller.

Reclaim is best-effort because its callers cannot abort teardown. Report
a quiesce failure locally, but always restore the default routing.

Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
Changes in v7:
  - Leave dmaengine channel selection and lifetime management to the
    endpoint function, per discussion with Frank on v6 patch 4.

 drivers/dma/dw-edma/dw-edma-core.c | 39 ++++++++++++++++++++++++++++++
 include/linux/dma/edma.h           | 11 +++++++++
 2 files changed, 50 insertions(+)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index d214df55da3c..1582ecfc2965 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -1303,6 +1303,45 @@ int dw_edma_remove(struct dw_edma_chip *chip)
 }
 EXPORT_SYMBOL_GPL(dw_edma_remove);
 
+int dw_edma_delegate_chan(struct dma_chan *dchan)
+{
+	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
+	int ret = 0;
+
+	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
+		return -EINVAL;
+
+	guard(spinlock_irqsave)(&chan->vc.lock);
+
+	if (chan->configured || chan->status != EDMA_ST_IDLE ||
+	    chan->request != EDMA_REQ_NONE)
+		ret = -EBUSY;
+	else
+		chan->irq_mode = DW_EDMA_CH_IRQ_REMOTE;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dw_edma_delegate_chan);
+
+void dw_edma_reclaim_chan(struct dma_chan *dchan, bool quiesce)
+{
+	struct dw_edma_chan *chan;
+
+	if (!dchan)
+		return;
+
+	chan = dchan2dw_edma_chan(dchan);
+	if (quiesce && dw_edma_core_ch_quiesce(chan))
+		dev_warn(chan->dw->chip->dev,
+			 "failed to quiesce delegated %s channel %u\n",
+			 chan->dir == EDMA_DIR_WRITE ? "write" : "read",
+			 chan->id);
+
+	scoped_guard(spinlock_irqsave, &chan->vc.lock)
+		chan->irq_mode = dw_edma_get_default_irq_mode(chan);
+}
+EXPORT_SYMBOL_GPL(dw_edma_reclaim_chan);
+
 MODULE_LICENSE("GPL v2");
 MODULE_DESCRIPTION("Synopsys DesignWare eDMA controller core driver");
 MODULE_AUTHOR("Gustavo Pimentel <gustavo.pimentel@xxxxxxxxxxxx>");
diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
index 3c8e2ef9dee0..61ebb808981e 100644
--- a/include/linux/dma/edma.h
+++ b/include/linux/dma/edma.h
@@ -153,6 +153,8 @@ struct dw_edma_chip {
 #if IS_REACHABLE(CONFIG_DW_EDMA)
 int dw_edma_probe(struct dw_edma_chip *chip);
 int dw_edma_remove(struct dw_edma_chip *chip);
+int dw_edma_delegate_chan(struct dma_chan *chan);
+void dw_edma_reclaim_chan(struct dma_chan *chan, bool quiesce);
 #else
 static inline int dw_edma_probe(struct dw_edma_chip *chip)
 {
@@ -163,6 +165,15 @@ static inline int dw_edma_remove(struct dw_edma_chip *chip)
 {
 	return 0;
 }
+
+static inline int dw_edma_delegate_chan(struct dma_chan *chan)
+{
+	return -ENODEV;
+}
+
+static inline void dw_edma_reclaim_chan(struct dma_chan *chan, bool quiesce)
+{
+}
 #endif /* CONFIG_DW_EDMA */
 
 #endif /* _DW_EDMA_H */
-- 
2.51.0