[PATCH v2 01/19] dmaengine: dw-edma: Add dw_edma_core_ll_cur_idx() to get current LL entry index

[Koichiro Den]

From: Frank Li <Frank.Li@xxxxxxx>

Add dw_edma_core_ll_cur_idx() to get the current LL entry index and
prepare for dynamic addition of DMA requests while the DMA engine is
running.

Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
Co-developed-by: Koichiro Den <den@xxxxxxxxxxxxx>
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
Based on Frank's original submission:
https://lore.kernel.org/dmaengine/20260109-edma_dymatic-v1-1-9a98c9c98536@xxxxxxx/

Changes in v2:
  - Handle zero low words and low-word wrap without reading DMA_LLP.MSB
    on the normal path, and clarify the lost-context comments.

 drivers/dma/dw-edma/dw-edma-core.h    | 10 ++++++++++
 drivers/dma/dw-edma/dw-edma-v0-core.c | 19 +++++++++++++++++++
 drivers/dma/dw-edma/dw-hdma-v0-core.c | 19 +++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/drivers/dma/dw-edma/dw-edma-core.h b/drivers/dma/dw-edma/dw-edma-core.h
index f6a5ad317567..e50fa7965778 100644
--- a/drivers/dma/dw-edma/dw-edma-core.h
+++ b/drivers/dma/dw-edma/dw-edma-core.h
@@ -138,6 +138,7 @@ struct dw_edma_core_ops {
 	void (*ll_data)(struct dw_edma_chan *chan, struct dw_edma_burst *burst,
 			u32 idx, bool cb, bool irq);
 	void (*ll_link)(struct dw_edma_chan *chan, u32 idx, bool cb, u64 addr);
+	int (*ll_cur_idx)(struct dw_edma_chan *chan);
 	void (*ch_doorbell)(struct dw_edma_chan *chan);
 	void (*ch_enable)(struct dw_edma_chan *chan);
 	void (*ch_config)(struct dw_edma_chan *chan);
@@ -181,6 +182,15 @@ struct dw_edma_chan *dchan2dw_edma_chan(struct dma_chan *dchan)
 	return vc2dw_edma_chan(to_virt_chan(dchan));
 }
 
+/*
+ * Return the current LL entry index. A negative value means that the channel
+ * context is not initialized or was lost after a link reset.
+ */
+static inline int dw_edma_core_ll_cur_idx(struct dw_edma_chan *chan)
+{
+	return chan->dw->core->ll_cur_idx(chan);
+}
+
 static inline u64 dw_edma_core_get_ll_paddr(struct dw_edma_chan *chan)
 {
 	if (chan->dir == EDMA_DIR_WRITE)
diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
index abc1bd4c0be2..ba84811234e1 100644
--- a/drivers/dma/dw-edma/dw-edma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
@@ -616,6 +616,24 @@ static void dw_edma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
 		  FIELD_PREP(EDMA_V0_DOORBELL_CH_MASK, chan->id));
 }
 
+static int dw_edma_v0_core_ll_cur_idx(struct dw_edma_chan *chan)
+{
+	u32 base, val;
+
+	val = GET_CH_32(chan->dw, chan->dir, chan->id, llp.lsb);
+	base = lower_32_bits(dw_edma_core_get_ll_paddr(chan));
+
+	/*
+	 * An all-zero pointer means that the channel context is unavailable,
+	 * so an LL region starting at DMA address zero is not supported.
+	 */
+	if (!val && !GET_CH_32(chan->dw, chan->dir, chan->id, llp.msb))
+		return -EINVAL;
+
+	/* u32 subtraction handles a low-word wrap at a 4 GiB boundary. */
+	return (val - base) / EDMA_LL_SZ;
+}
+
 /* eDMA debugfs callbacks */
 static void dw_edma_v0_core_debugfs_on(struct dw_edma *dw)
 {
@@ -650,6 +668,7 @@ static const struct dw_edma_core_ops dw_edma_v0_core = {
 	.handle_int = dw_edma_v0_core_handle_int,
 	.ll_data = dw_edma_v0_core_ll_data,
 	.ll_link = dw_edma_v0_core_ll_link,
+	.ll_cur_idx = dw_edma_v0_core_ll_cur_idx,
 	.ch_doorbell = dw_edma_v0_core_ch_doorbell,
 	.ch_enable = dw_edma_v0_core_ch_enable,
 	.ch_config = dw_edma_v0_core_ch_config,
diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
index 36ee72efcd31..2fc7f8e85b43 100644
--- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
@@ -384,6 +384,24 @@ static void dw_hdma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
 	SET_CH_32(dw, chan->dir, chan->id, doorbell, HDMA_V0_DOORBELL_START);
 }
 
+static int dw_hdma_v0_core_ll_cur_idx(struct dw_edma_chan *chan)
+{
+	u32 base, val;
+
+	val = GET_CH_32(chan->dw, chan->dir, chan->id, llp.lsb);
+	base = lower_32_bits(dw_edma_core_get_ll_paddr(chan));
+
+	/*
+	 * An all-zero pointer means that the channel context is unavailable,
+	 * so an LL region starting at DMA address zero is not supported.
+	 */
+	if (!val && !GET_CH_32(chan->dw, chan->dir, chan->id, llp.msb))
+		return -EINVAL;
+
+	/* u32 subtraction handles a low-word wrap at a 4 GiB boundary. */
+	return (val - base) / EDMA_LL_SZ;
+}
+
 /* HDMA debugfs callbacks */
 static void dw_hdma_v0_core_debugfs_on(struct dw_edma *dw)
 {
@@ -406,6 +424,7 @@ static const struct dw_edma_core_ops dw_hdma_v0_core = {
 	.non_ll_start = dw_hdma_v0_core_non_ll_start,
 	.ll_data = dw_hdma_v0_core_ll_data,
 	.ll_link = dw_hdma_v0_core_ll_link,
+	.ll_cur_idx = dw_hdma_v0_core_ll_cur_idx,
 	.ch_doorbell = dw_hdma_v0_core_ch_doorbell,
 	.ch_enable = dw_hdma_v0_core_ch_enable,
 	.ch_config = dw_hdma_v0_core_ch_config,
-- 
2.51.0