[PATCH v2 2/3] dmaengine: dw-edma: Configure remote interrupt routing

[Koichiro Den <den@valinux.co.jp>]

An endpoint function can reserve an endpoint-local channel while the RC
programs it through an exposed register window. Such a channel must route
interrupts remotely and ignore them on the endpoint.

Use dma_slave_config to set enum dw_edma_ch_irq_mode on idle channels of a
local eDMA-compatible instance. Synchronizing a remote-routed channel
quiesces the hardware, after which the caller can restore its routing and
release it.

The eDMA quiesce may stop a complete direction. The caller must own every
channel in that direction and stop remote programming first.

Suggested-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
Changes in v2:
  - Rework the channel routing from PCI DMA EPF v7 patches 5 and 6.
    https://lore.kernel.org/r/20260813063757.3131865-6-den@valinux.co.jp/
    https://lore.kernel.org/r/20260813063757.3131865-7-den@valinux.co.jp/
  - Use dma_slave_config instead of private delegation helpers. (Frank)
    https://lore.kernel.org/r/ao2nHoCwfTEEiFSr@SMW015318/

 drivers/dma/dw-edma/dw-edma-core.c | 51 +++++++++++++++++++++++++++---
 include/linux/dma/edma.h           |  6 ++++
 2 files changed, 52 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index a678c70a78fe..a8c6bd508fcd 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -177,6 +177,30 @@ dw_edma_get_default_irq_mode(struct dw_edma_chan *chan)
 						  DW_EDMA_CH_IRQ_REMOTE;
 }
 
+static int dw_edma_device_config_irq_mode(struct dw_edma_chan *chan,
+					  struct dma_slave_config *config)
+{
+	enum dw_edma_ch_irq_mode mode;
+
+	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL) ||
+	    config->peripheral_size != sizeof(mode))
+		return -EINVAL;
+
+	mode = *(enum dw_edma_ch_irq_mode *)config->peripheral_config;
+	if (mode != DW_EDMA_CH_IRQ_LOCAL && mode != DW_EDMA_CH_IRQ_REMOTE)
+		return -EINVAL;
+
+	guard(spinlock_irqsave)(&chan->vc.lock);
+
+	if (chan->configured || chan->status != EDMA_ST_IDLE ||
+	    chan->request != EDMA_REQ_NONE)
+		return -EBUSY;
+
+	chan->irq_mode = mode;
+
+	return 0;
+}
+
 static int dw_edma_device_config(struct dma_chan *dchan,
 				 struct dma_slave_config *config)
 {
@@ -184,6 +208,10 @@ static int dw_edma_device_config(struct dma_chan *dchan,
 	bool cfg_non_ll;
 	int non_ll = 0;
 
+	if (chan->dw->chip->mf != EDMA_MF_HDMA_NATIVE &&
+	    config->peripheral_config)
+		return dw_edma_device_config_irq_mode(chan, config);
+
 	chan->non_ll = false;
 	if (chan->dw->chip->mf == EDMA_MF_HDMA_NATIVE) {
 		if (config->peripheral_config &&
@@ -213,10 +241,6 @@ static int dw_edma_device_config(struct dma_chan *dchan,
 
 		if (cfg_non_ll || non_ll)
 			chan->non_ll = true;
-	} else if (config->peripheral_config) {
-		dev_err(dchan->device->dev,
-			"peripheral config param applicable only for HDMA\n");
-		return -EINVAL;
 	}
 
 	memcpy(&chan->config, config, sizeof(*config));
@@ -893,6 +917,17 @@ static void dw_edma_wait_termination(struct dma_chan *dchan)
 static void dw_edma_device_synchronize(struct dma_chan *dchan)
 {
 	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
+	bool remote;
+
+	scoped_guard(spinlock_irqsave, &chan->vc.lock)
+		remote = chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL &&
+			 chan->irq_mode == DW_EDMA_CH_IRQ_REMOTE;
+
+	if (remote && dw_edma_core_ch_quiesce(chan))
+		dev_warn(chan->dw->chip->dev,
+			 "failed to quiesce remote-routed %s channel %u\n",
+			 chan->dir == EDMA_DIR_WRITE ? "write" : "read",
+			 chan->id);
 
 	dw_edma_wait_termination(dchan);
 	cancel_work_sync(&chan->irq_work);
@@ -903,12 +938,18 @@ static void dw_edma_device_synchronize(struct dma_chan *dchan)
 static void dw_edma_free_chan_resources(struct dma_chan *dchan)
 {
 	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
+	enum dw_edma_ch_irq_mode default_mode =
+			dw_edma_get_default_irq_mode(chan);
 
 	dw_edma_device_terminate_all(dchan);
 	dw_edma_device_synchronize(dchan);
 
-	scoped_guard(spinlock_irqsave, &chan->vc.lock)
+	scoped_guard(spinlock_irqsave, &chan->vc.lock) {
 		chan->configured = false;
+		/* Avoid a redundant write racing with shared-IRQ readers. */
+		if (chan->irq_mode != default_mode)
+			chan->irq_mode = default_mode;
+	}
 
 	vchan_free_chan_resources(&chan->vc);
 }
diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
index 3c8e2ef9dee0..54491c9e4b5e 100644
--- a/include/linux/dma/edma.h
+++ b/include/linux/dma/edma.h
@@ -92,6 +92,12 @@ enum dw_edma_chip_flags {
  * handed over to and driven by the remote side, and the recipe above is
  * applied by the driving instance.
  *
+ * On a local eDMA-compatible instance, clients may pass this enum through
+ * dma_slave_config.peripheral_config to switch an idle, unconfigured channel
+ * between LOCAL and REMOTE routing. Before synchronizing a REMOTE channel,
+ * the client must stop remote programming and own every channel affected by
+ * the hardware quiesce.
+ *
  * HDMA linked-list watermark interrupts have the same LWIE/RWIE guidance. HDMA
  * non-linked-list mode has dedicated local and remote stop/abort interrupt
  * enables.
-- 
2.51.0