[PATCH v4 05/14] dmaengine: dw-edma: Add partial channel ownership mode

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

A DesignWare eDMA instance may represent only a subset of channels that
is also initialized by another OS instance, such as an endpoint-side OS.
Add a partial ownership flag for instances that must preserve
controller-wide state owned by that peer.

In partial ownership mode, dw-edma skips the initial core reset and uses
the limited quiesce path in probe() and remove() instead of the full
core-off path. The flag also makes the driver validate the ownership
granularity required by each register layout before registering
channels.

Partial instances also skip interrupt-emulation doorbell allocation: the
emulated doorbell is a controller-level resource, and a partial owner
must not claim it on behalf of the whole block.

For EDMA_MF_EDMA_UNROLL and EDMA_MF_HDMA_COMPAT, the driver programs
per-direction registers, such as DMA_{WRITE,READ}_INT_MASK_OFF and
DMA_{WRITE,READ}_INT_CLEAR_OFF. These register layouts have at most
EDMA_MAX_{WR,RD}_CH channels per direction, so the capped hardware
channel count still represents the whole direction. A partial instance
can therefore expose write or read channels only if it owns every
channel in that direction; otherwise two OS instances could update the
same direction-wide registers without a shared locking protocol.

In contrast, HDMA native uses per-channel registers, so it can be owned
at channel granularity.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
Changes in v4:
  - Fix and revise commit message. (Frank)
  - Move partial-ownership validation into dw_edma_check_partial().
    (Frank)
  - While at it, add a small source comment that explains why local
    variables hw_{wr,rd}_ch_cnt are introduced separately.
  - Quiesce represented resources during partial probe as well as
    remove, draining stale channel state from a previous owner without
    resetting controller-wide state.

 drivers/dma/dw-edma/dw-edma-core.c | 75 ++++++++++++++++++++++++++----
 include/linux/dma/edma.h           |  7 +++
 2 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index fb17074917df..0d38de4480a0 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -831,6 +831,9 @@ static int dw_edma_emul_irq_alloc(struct dw_edma *dw)
 	chip->db_irq = 0;
 	chip->db_offset = ~0;
 
+	if (chip->flags & DW_EDMA_CHIP_PARTIAL)
+		return 0;
+
 	/*
 	 * Only meaningful when the core provides the deassert sequence
 	 * for interrupt emulation.
@@ -1188,10 +1191,33 @@ static int dw_edma_irq_request(struct dw_edma *dw,
 	return err;
 }
 
+static int dw_edma_check_partial(struct dw_edma_chip *chip,
+				 u16 hw_wr_ch_cnt, u16 hw_rd_ch_cnt)
+{
+	if (!(chip->flags & DW_EDMA_CHIP_PARTIAL))
+		return 0;
+
+	if (chip->mf != EDMA_MF_EDMA_UNROLL &&
+	    chip->mf != EDMA_MF_HDMA_COMPAT)
+		return 0;
+
+	/*
+	 * Direction-wide registers are shared by all channels in that
+	 * direction, so a direction must have a single owner.
+	 */
+	if ((chip->ll_wr_cnt && chip->ll_wr_cnt != hw_wr_ch_cnt) ||
+	    (chip->ll_rd_cnt && chip->ll_rd_cnt != hw_rd_ch_cnt))
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+
 int dw_edma_probe(struct dw_edma_chip *chip)
 {
 	struct device *dev;
 	struct dw_edma *dw;
+	u16 hw_wr_ch_cnt;
+	u16 hw_rd_ch_cnt;
 	u32 wr_alloc = 0;
 	u32 rd_alloc = 0;
 	int i, err;
@@ -1203,6 +1229,17 @@ int dw_edma_probe(struct dw_edma_chip *chip)
 	if (!dev || !chip->ops)
 		return -EINVAL;
 
+	if (chip->flags & DW_EDMA_CHIP_PARTIAL) {
+		switch (chip->mf) {
+		case EDMA_MF_EDMA_UNROLL:
+		case EDMA_MF_HDMA_COMPAT:
+		case EDMA_MF_HDMA_NATIVE:
+			break;
+		default:
+			return -EOPNOTSUPP;
+		}
+	}
+
 	dw = devm_kzalloc(dev, sizeof(*dw), GFP_KERNEL);
 	if (!dw)
 		return -ENOMEM;
@@ -1216,13 +1253,21 @@ int dw_edma_probe(struct dw_edma_chip *chip)
 
 	raw_spin_lock_init(&dw->lock);
 
-	dw->wr_ch_cnt = min_t(u16, chip->ll_wr_cnt,
-			      dw_edma_core_ch_count(dw, EDMA_DIR_WRITE));
-	dw->wr_ch_cnt = min_t(u16, dw->wr_ch_cnt, EDMA_MAX_WR_CH);
+	/*
+	 * chip->ll_*_cnt describes the channels exposed by this instance. Keep
+	 * the usable hardware counts separate for partial ownership checks.
+	 */
+	hw_wr_ch_cnt = min_t(u16, dw_edma_core_ch_count(dw, EDMA_DIR_WRITE),
+			     EDMA_MAX_WR_CH);
+	hw_rd_ch_cnt = min_t(u16, dw_edma_core_ch_count(dw, EDMA_DIR_READ),
+			     EDMA_MAX_RD_CH);
+
+	err = dw_edma_check_partial(chip, hw_wr_ch_cnt, hw_rd_ch_cnt);
+	if (err)
+		return err;
 
-	dw->rd_ch_cnt = min_t(u16, chip->ll_rd_cnt,
-			      dw_edma_core_ch_count(dw, EDMA_DIR_READ));
-	dw->rd_ch_cnt = min_t(u16, dw->rd_ch_cnt, EDMA_MAX_RD_CH);
+	dw->wr_ch_cnt = min_t(u16, chip->ll_wr_cnt, hw_wr_ch_cnt);
+	dw->rd_ch_cnt = min_t(u16, chip->ll_rd_cnt, hw_rd_ch_cnt);
 
 	if (!dw->wr_ch_cnt && !dw->rd_ch_cnt)
 		return -EINVAL;
@@ -1239,8 +1284,16 @@ int dw_edma_probe(struct dw_edma_chip *chip)
 	snprintf(dw->name, sizeof(dw->name), "dw-edma-core:%s",
 		 dev_name(chip->dev));
 
-	/* Disable eDMA, only to establish the ideal initial conditions */
-	dw_edma_core_off(dw);
+	if (chip->flags & DW_EDMA_CHIP_PARTIAL) {
+		/*
+		 * Do not reset the shared controller, but drain stale state
+		 * from resources represented by this instance.
+		 */
+		dw_edma_core_quiesce(dw);
+	} else {
+		/* Disable eDMA only when this instance owns the controller. */
+		dw_edma_core_off(dw);
+	}
 
 	/*
 	 * Deferred IRQ works are queued from the hard IRQ handlers, so the
@@ -1296,8 +1349,10 @@ int dw_edma_remove(struct dw_edma_chip *chip)
 	if (!dw)
 		return -ENODEV;
 
-	/* Disable eDMA */
-	dw_edma_core_off(dw);
+	if (chip->flags & DW_EDMA_CHIP_PARTIAL)
+		dw_edma_core_quiesce(dw);
+	else
+		dw_edma_core_off(dw);
 
 	/* Free irqs */
 	for (i = (dw->nr_irqs - 1); i >= 0; i--)
diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
index 1007122d4123..3c33d12d1cdb 100644
--- a/include/linux/dma/edma.h
+++ b/include/linux/dma/edma.h
@@ -55,9 +55,16 @@ enum dw_edma_map_format {
 /**
  * enum dw_edma_chip_flags - Flags specific to an eDMA chip
  * @DW_EDMA_CHIP_LOCAL:		eDMA is used locally by an endpoint
+ * @DW_EDMA_CHIP_PARTIAL:	Only channels described by this instance are
+ *				owned by this driver. Controller-wide state
+ *				must be preserved, and layouts with shared
+ *				direction-wide registers must only be shared at
+ *				direction granularity. Layouts with per-channel
+ *				registers may be shared at channel granularity.
  */
 enum dw_edma_chip_flags {
 	DW_EDMA_CHIP_LOCAL	= BIT(0),
+	DW_EDMA_CHIP_PARTIAL	= BIT(1),
 };
 
 /**
-- 
2.51.0