[PATCH] misc: fastrpc: create duplicate sessions after all CB probing

[Vinayak Katoch]

For ADSP, only a limited number of FastRPC context banks (CBs) are
available. Each CB supports a single session, which means only a few
processes can run on ADSP simultaneously. If all sessions are consumed
by fastrpc daemons, no session remains available when a user application
starts, causing the application to fail.

To address this limitation, a Device Tree change was used till now:
  qcom,nsessions = <5>;

However, feedback from the upstream community indicated that this change
should not be made in the Device Tree. Instead, it was recommended to
handle this as a driver-level change.

Instead of duplicating sessions inline during fastrpc_cb_probe() using
the qcom,nsessions DT property, defer duplication until after
of_platform_populate() returns in fastrpc_rpmsg_probe(), at which point
all compute-CB child nodes have been probed and the session array is
fully populated.

For the ADSP domain, append FASTRPC_DUP_SESSIONS (4) copies of the
last probed session once of_platform_populate() succeeds. This keeps
the per-CB probe path simple and ensures duplicates are always derived
from a stable, fully-initialised session state.

The qcom,nsessions DT property is no longer consumed by the driver; the
binding and DT sources are left unchanged.

Signed-off-by: Vinayak Katoch <vinayak.katoch@xxxxxxxxxxxxxxxx>
---
 drivers/misc/fastrpc.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 1080f9acf70a..46afbae9c234 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -30,6 +30,7 @@
 #define CDSP_DOMAIN_ID (3)
 #define GDSP_DOMAIN_ID (4)
 #define FASTRPC_MAX_SESSIONS	14
+#define FASTRPC_DUP_SESSIONS	4
 #define FASTRPC_MAX_VMIDS	16
 #define FASTRPC_ALIGN		128
 #define FASTRPC_MAX_FDLIST	16
@@ -2195,7 +2196,6 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
 	struct fastrpc_channel_ctx *cctx;
 	struct fastrpc_session_ctx *sess;
 	struct device *dev = &pdev->dev;
-	int i, sessions = 0;
 	unsigned long flags;
 	int rc;
 	u32 dma_bits;
@@ -2204,8 +2204,6 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
 	if (!cctx)
 		return -EINVAL;
 
-	of_property_read_u32(dev->of_node, "qcom,nsessions", &sessions);
-
 	spin_lock_irqsave(&cctx->lock, flags);
 	if (cctx->sesscount >= FASTRPC_MAX_SESSIONS) {
 		dev_err(&pdev->dev, "too many sessions\n");
@@ -2225,16 +2223,6 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
 	if (of_property_read_u32(dev->of_node, "reg", &sess->sid))
 		dev_info(dev, "FastRPC Session ID not specified in DT\n");
 
-	if (sessions > 0) {
-		struct fastrpc_session_ctx *dup_sess;
-
-		for (i = 1; i < sessions; i++) {
-			if (cctx->sesscount >= FASTRPC_MAX_SESSIONS)
-				break;
-			dup_sess = &cctx->session[cctx->sesscount++];
-			memcpy(dup_sess, sess, sizeof(*dup_sess));
-		}
-	}
 	spin_unlock_irqrestore(&cctx->lock, flags);
 	rc = dma_set_mask(dev, DMA_BIT_MASK(dma_bits));
 	if (rc) {
@@ -2445,6 +2433,23 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 	if (err)
 		goto err_deregister_fdev;
 
+	if (data->domain_id == ADSP_DOMAIN_ID && data->sesscount > 0) {
+		struct fastrpc_session_ctx *last_sess;
+		struct fastrpc_session_ctx *dup_sess;
+		unsigned long flags;
+		int i;
+
+		spin_lock_irqsave(&data->lock, flags);
+		last_sess = &data->session[data->sesscount - 1];
+		for (i = 0; i < FASTRPC_DUP_SESSIONS; i++) {
+			if (data->sesscount >= FASTRPC_MAX_SESSIONS)
+				break;
+			dup_sess = &data->session[data->sesscount++];
+			memcpy(dup_sess, last_sess, sizeof(*dup_sess));
+		}
+		spin_unlock_irqrestore(&data->lock, flags);
+	}
+
 	return 0;
 
 err_deregister_fdev:

---
base-commit: 97e797263a5e963da3d1e66e743fd518567dfe37
change-id: 20260609-dup-sessions-ea2acaac1994

Best regards,
-- 
Vinayak Katoch <vinayak.katoch@xxxxxxxxxxxxxxxx>