[PATCH 19/23] dmaengine: sdxi: Provide context start and stop APIs

[Nathan Lynch <nathan.lynch@amd.com>]

Starting and stopping SDXI client contexts is implemented by submitting
special-purpose descriptors to a function's admin context.

Introduce high-level context start and stop APIs that operate on
struct sdxi_cxt objects, encapsulating the administrative descriptor
submission and completion signaling. These are intended for use by
clients such as the DMA engine provider to come.

Co-developed-by: Wei Huang <wei.huang2@amd.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>
---
 drivers/dma/sdxi/context.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++
 drivers/dma/sdxi/context.h |  3 ++
 2 files changed, 80 insertions(+)

diff --git a/drivers/dma/sdxi/context.c b/drivers/dma/sdxi/context.c
index 04e0d3e6a337..fc6291f12ffe 100644
--- a/drivers/dma/sdxi/context.c
+++ b/drivers/dma/sdxi/context.c
@@ -23,7 +23,9 @@
 #include <asm/barrier.h>
 #include <asm/rwonce.h>
 
+#include "completion.h"
 #include "context.h"
+#include "descriptor.h"
 #include "hw.h"
 #include "ring.h"
 #include "sdxi.h"
@@ -394,6 +396,81 @@ int sdxi_admin_cxt_init(struct sdxi_dev *sdxi)
 	return devm_add_action_or_reset(sdxi_to_dev(sdxi), free_admin_cxt, sdxi);
 }
 
+int sdxi_start_cxt(struct sdxi_cxt *cxt)
+{
+	struct sdxi_cxt *adm = to_admin_cxt(cxt);
+	struct sdxi_desc *desc;
+	struct sdxi_ring_resv resv;
+	int err;
+
+	might_sleep();
+
+	struct sdxi_completion *sc __free(sdxi_completion) =
+		sdxi_completion_alloc(cxt->sdxi);
+
+	if (!sc)
+		return -ENOMEM;
+
+	/* This is not how to start the admin context. */
+	if (WARN_ON(adm == cxt))
+		return -EINVAL;
+
+	err = sdxi_ring_reserve(adm->ring_state, 1, &resv);
+	if (err)
+		return err;
+
+	desc = sdxi_ring_resv_next(&resv);
+	sdxi_encode_cxt_start(desc, &(const struct sdxi_cxt_start) {
+			.range = sdxi_cxt_range_single(cxt->id),
+		});
+	sdxi_completion_attach(desc, sc);
+	sdxi_desc_make_valid(desc);
+	sdxi_cxt_push_doorbell(adm, sdxi_ring_resv_dbval(&resv));
+	sdxi_completion_poll(sc);
+
+	return 0;
+}
+
+void sdxi_stop_cxt(struct sdxi_cxt *cxt)
+{
+	struct sdxi_cxt *adm = to_admin_cxt(cxt);
+	struct sdxi_desc *stop, *sync;
+	struct sdxi_ring_resv resv;
+	int err;
+
+	might_sleep();
+
+	struct sdxi_completion *sc __free(sdxi_completion) =
+		sdxi_completion_alloc(cxt->sdxi);
+
+	if (!sc)
+		return;
+
+	/* This is not how to stop the admin context. */
+	if (WARN_ON(adm == cxt))
+		return;
+
+	err = sdxi_ring_reserve(adm->ring_state, 2, &resv);
+	if (WARN_ON_ONCE(err))
+		return;
+
+	stop = sdxi_ring_resv_next(&resv);
+	sync = sdxi_ring_resv_next(&resv);
+
+	sdxi_encode_cxt_stop(stop, &(const struct sdxi_cxt_stop) {
+			.range = sdxi_cxt_range_single(cxt->id),
+		});
+	sdxi_encode_sync(sync, &(const struct sdxi_sync) {
+			.filter = SDXI_SYNC_FLT_STOP,
+			.range = sdxi_cxt_range_single(cxt->id),
+		});
+	sdxi_completion_attach(sync, sc);
+	sdxi_desc_make_valid(stop);
+	sdxi_desc_make_valid(sync);
+	sdxi_cxt_push_doorbell(adm, sdxi_ring_resv_dbval(&resv));
+	sdxi_completion_poll(sc);
+}
+
 /*
  * Allocate a context for in-kernel use. Starting the context is the
  * caller's responsibility.
diff --git a/drivers/dma/sdxi/context.h b/drivers/dma/sdxi/context.h
index 5310e51a668c..9061221e86cb 100644
--- a/drivers/dma/sdxi/context.h
+++ b/drivers/dma/sdxi/context.h
@@ -67,6 +67,9 @@ int sdxi_admin_cxt_init(struct sdxi_dev *sdxi);
 struct sdxi_cxt *sdxi_cxt_new(struct sdxi_dev *sdxi);
 void sdxi_cxt_exit(struct sdxi_cxt *cxt);
 
+int sdxi_start_cxt(struct sdxi_cxt *cxt);
+void sdxi_stop_cxt(struct sdxi_cxt *cxt);
+
 static inline struct sdxi_cxt *to_admin_cxt(const struct sdxi_cxt *cxt)
 {
 	return cxt->sdxi->admin_cxt;

-- 
2.53.0