[PATCH 3/3] dmaengine: drop DMA_COMPLETION_NO_ORDER and DMA_OUT_OF_ORDER

[Daniel Byrne <daniel1.byrne@intel.com>]

DMA_COMPLETION_NO_ORDER (commit 47ec7f09bc10 ("dmaengine: cookie bypass
for out of order completion")) flagged devices whose completions can
overtake submission order. On DSA this happens when a work queue (one
dmaengine channel) belongs to a group that contains several engines.
Per-channel cookie tracking gives wrong answers in this case, since
dma_cookie_complete() moves the completed-cookie watermark past
still-in-flight earlier descriptors, so cookie-order status can report
DMA_COMPLETE for a running transfer. Clients were told to use
callbacks only, dmatest refused polled mode, and DMA_OUT_OF_ORDER
existed as the tx_status answer for such devices.

idxd, the only in-tree setter, now answers
dmaengine_async_is_tx_complete() from per-descriptor generation
numbers, exactly within the limits that helper's kernel-doc states: for
a transaction submitted without DMA_PREP_INTERRUPT, on the first query
that reports it finished. Polling an out-of-order device is therefore
safe and neither the capability nor the status code has any remaining
meaning. Drop them.

Whether reordering occurs at all is group configuration rather than a
device property. A group with a single engine completes its work
queues' descriptors in order. However, the driver cannot assume how
the administrator grouped engines, and the all-engines-in-one-group
layout is the device's throughput configuration.

Assisted-by: Claude:claude-opus-5-5
Assisted-by: Claude:claude-fable-5-1
Signed-off-by: Daniel Byrne <daniel1.byrne@intel.com>
---
 .../driver-api/dmaengine/provider.rst         | 19 -------------------
 drivers/dma/dmatest.c                         | 11 +----------
 drivers/dma/idxd/dma.c                        |  1 -
 include/linux/dmaengine.h                     |  5 +----
 4 files changed, 2 insertions(+), 34 deletions(-)

diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
index ef342886af96..435ccd3bedac 100644
--- a/Documentation/driver-api/dmaengine/provider.rst
+++ b/Documentation/driver-api/dmaengine/provider.rst
@@ -260,22 +260,6 @@ Currently, the types available are:
     want to transfer a portion of uncompressed data directly to the
     display to print it
 
-- DMA_COMPLETION_NO_ORDER
-
-  - The device does not support in order completion.
-
-  - The driver should return DMA_OUT_OF_ORDER for device_tx_status if
-    the device is setting this capability.
-
-  - All cookie tracking and checking API should be treated as invalid if
-    the device exports this capability.
-
-  - At this point, this is incompatible with polling option for dmatest.
-
-  - If this cap is set, the user is recommended to provide an unique
-    identifier for each descriptor sent to the DMA device in order to
-    properly track the completion.
-
 - DMA_REPEAT
 
   - The device supports repeated transfers. A repeated transfer, indicated by
@@ -468,9 +452,6 @@ supported.
   - In the case of a cyclic transfer, it should only take into
     account the total size of the cyclic buffer.
 
-  - Should return DMA_OUT_OF_ORDER if the device does not support in order
-    completion and is completing the operation out of order.
-
   - This function can be called in an interrupt context.
 
 - device_config
diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c
index 3d0d54a97add..fbfa2f1d6f29 100644
--- a/drivers/dma/dmatest.c
+++ b/drivers/dma/dmatest.c
@@ -854,10 +854,7 @@ static int dmatest_func(void *data)
 			result("test timed out", total_tests, src->off, dst->off,
 			       len, 0);
 			goto error_unmap_continue;
-		} else if (status != DMA_COMPLETE &&
-			   !(dma_has_cap(DMA_COMPLETION_NO_ORDER,
-					 dev->cap_mask) &&
-			     status == DMA_OUT_OF_ORDER)) {
+		} else if (status != DMA_COMPLETE) {
 			result(status == DMA_ERROR ?
 			       "completion error status" :
 			       "completion busy status", total_tests, src->off,
@@ -1035,12 +1032,6 @@ static int dmatest_add_channel(struct dmatest_info *info,
 	dtc->chan = chan;
 	INIT_LIST_HEAD(&dtc->threads);
 
-	if (dma_has_cap(DMA_COMPLETION_NO_ORDER, dma_dev->cap_mask) &&
-	    info->params.polled) {
-		info->params.polled = false;
-		pr_warn("DMA_COMPLETION_NO_ORDER, polled disabled\n");
-	}
-
 	if (dma_has_cap(DMA_MEMCPY, dma_dev->cap_mask)) {
 		if (dmatest == 0) {
 			cnt = dmatest_add_threads(info, dtc, DMA_MEMCPY);
diff --git a/drivers/dma/idxd/dma.c b/drivers/dma/idxd/dma.c
index dd5a9d9274ce..19340c7ae2d3 100644
--- a/drivers/dma/idxd/dma.c
+++ b/drivers/dma/idxd/dma.c
@@ -417,7 +417,6 @@ int idxd_register_dma_device(struct idxd_device *idxd)
 
 	dma_cap_set(DMA_INTERRUPT, dma->cap_mask);
 	dma_cap_set(DMA_PRIVATE, dma->cap_mask);
-	dma_cap_set(DMA_COMPLETION_NO_ORDER, dma->cap_mask);
 	dma->device_release = idxd_dma_release;
 
 	dma->device_prep_dma_interrupt = idxd_dma_prep_interrupt;
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 83bef7a70b99..9f73470759bb 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -39,7 +39,6 @@ enum dma_status {
 	DMA_IN_PROGRESS,
 	DMA_PAUSED,
 	DMA_ERROR,
-	DMA_OUT_OF_ORDER,
 };
 
 /**
@@ -62,7 +61,6 @@ enum dma_transaction_type {
 	DMA_SLAVE,
 	DMA_CYCLIC,
 	DMA_INTERLEAVE,
-	DMA_COMPLETION_NO_ORDER,
 	DMA_REPEAT,
 	DMA_LOAD_EOT,
 /* last transaction type for creation of the capabilities mask */
@@ -1632,8 +1630,7 @@ static inline enum dma_status dma_async_is_tx_complete(struct dma_chan *chan,
  * has finished. Once the first terminal answer has retired the
  * descriptor, a later query for the same cookie reads DMA_COMPLETE.
  *
- * Return: DMA_COMPLETE, DMA_IN_PROGRESS, DMA_PAUSED, DMA_ERROR or
- * DMA_OUT_OF_ORDER.
+ * Return: DMA_COMPLETE, DMA_IN_PROGRESS, DMA_PAUSED or DMA_ERROR.
  */
 static inline enum dma_status dmaengine_async_is_tx_complete(struct dma_chan *chan,
 	dma_cookie_t cookie)
-- 
2.43.0