[PATCH v3 2/5] misc: fastrpc: Add polling mode support for fastRPC driver

[Ekansh Gupta]

For any remote call to DSP, after sending an invocation message,
fastRPC driver waits for glink response and during this time the
CPU can go into low power modes. Adding a polling mode support
with which fastRPC driver will poll continuously on a memory
after sending a message to remote subsystem which will eliminate
CPU wakeup and scheduling latencies and reduce fastRPC overhead.
With this change, DSP always sends a glink response which will
get ignored if polling mode didn't time out.

Signed-off-by: Ekansh Gupta <quic_ekangupt@xxxxxxxxxxx>
---
Changes in v3:
  - Rebase the patch to latest kernel version

 drivers/misc/fastrpc.c | 49 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 6b6ac3e3328d..4f8ecfcdf89f 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -109,6 +109,8 @@
 #define FASTRPC_RSP_VERSION2 2
 /* Early wake up poll completion number received from remoteproc */
 #define FASTRPC_EARLY_WAKEUP_POLL (0xabbccdde)
+/* Poll response number from remote processor for call completion */
+#define FASTRPC_POLL_RESPONSE (0xdecaf)
 /* timeout in us for polling until memory barrier */
 #define FASTRPC_POLL_TIME_MEM_UPDATE (500)
 /* timeout in us for busy polling after early response from remoteproc */
@@ -380,10 +382,14 @@ struct fastrpc_user {
 	struct fastrpc_buf *init_mem;
 
 	u32 profile;
+	/* Threads poll for specified timeout and fall back to glink wait */
+	u32 poll_timeout;
 	int tgid;
 	int pd;
 	bool is_secure_dev;
 	bool sharedcb;
+	/* If set, threads will poll for DSP response instead of glink wait */
+	bool poll_mode;
 	/* Lock for lists */
 	spinlock_t lock;
 	/* lock for allocations */
@@ -1376,6 +1382,11 @@ static int poll_for_remote_response(struct fastrpc_invoke_ctx *ctx, u32 timeout)
 			/* Remote processor sent early response */
 			err = 0;
 			break;
+		} else if (*poll == FASTRPC_POLL_RESPONSE) {
+			err = 0;
+			ctx->is_work_done = true;
+			ctx->retval = 0;
+			break;
 		}
 		if (jj == FASTRPC_POLL_TIME_MEM_UPDATE) {
 			/* Wait for DSP to finish updating poll memory */
@@ -1451,6 +1462,15 @@ static void fastrpc_wait_for_completion(struct fastrpc_invoke_ctx *ctx,
 			if (*ptr_interrupted || ctx->is_work_done)
 				return;
 			break;
+		case POLL_MODE:
+			err = poll_for_remote_response(ctx, ctx->fl->poll_timeout);
+
+			/* If polling timed out, move to normal response state */
+			if (err)
+				ctx->rsp_flags = NORMAL_RESPONSE;
+			else
+				*ptr_interrupted = 0;
+			break;
 		default:
 			*ptr_interrupted = -EBADR;
 			dev_err(ctx->fl->sctx->dev, "unsupported response type:0x%x\n", ctx->rsp_flags);
@@ -2065,6 +2085,32 @@ static int fastrpc_invoke(struct fastrpc_user *fl, char __user *argp)
 	return err;
 }
 
+static int fastrpc_manage_poll_mode(struct fastrpc_user *fl, u32 enable, u32 timeout)
+{
+	const unsigned int MAX_POLL_TIMEOUT_US = 10000;
+
+	if ((fl->cctx->domain_id != CDSP_DOMAIN_ID) || (fl->pd != USER_PD)) {
+		dev_err(&fl->cctx->rpdev->dev, "poll mode only allowed for dynamic CDSP process\n");
+		return -EPERM;
+	}
+	if (timeout > MAX_POLL_TIMEOUT_US) {
+		dev_err(&fl->cctx->rpdev->dev, "poll timeout %u is greater than max allowed value %u\n",
+			timeout, MAX_POLL_TIMEOUT_US);
+		return -EBADMSG;
+	}
+	spin_lock(&fl->lock);
+	if (enable) {
+		fl->poll_mode = true;
+		fl->poll_timeout = timeout;
+	} else {
+		fl->poll_mode = false;
+		fl->poll_timeout = 0;
+	}
+	spin_unlock(&fl->lock);
+	dev_info(&fl->cctx->rpdev->dev, "updated poll mode to %d, timeout %u\n", enable, timeout);
+	return 0;
+}
+
 static int fastrpc_internal_control(struct fastrpc_user *fl,
 					struct fastrpc_internal_control *cp)
 {
@@ -2079,6 +2125,9 @@ static int fastrpc_internal_control(struct fastrpc_user *fl,
 	case FASTRPC_CONTROL_SMMU:
 		fl->sharedcb = cp->smmu.sharedcb;
 		break;
+	case FASTRPC_CONTROL_RPC_POLL:
+		err = fastrpc_manage_poll_mode(fl, cp->lp.enable, cp->lp.latency);
+		break;
 	default:
 		err = -EBADRQC;
 		break;
-- 
2.17.1