[PATCH v1 4/4] misc: fastrpc: Add polling mode support for fastRPC driver

Ekansh Gupta
2024-10-07T08:45:48Z

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@quicinc.com>
---
drivers/misc/fastrpc.c | 127 +++++++++++++++++++++++++++++++++---
include/uapi/misc/fastrpc.h | 3 +-
2 files changed, 121 insertions(+), 9 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index c008fcd95e15..a25673c22db8 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -111,6 +111,19 @@
#define FASTRPC_KERNEL_PERF_LIST (PERF_KEY_MAX)
#define FASTRPC_DSP_PERF_LIST 12

+/* 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)
+
+/* Response types supported for RPC calls */
+enum fastrpc_response_flags {
+ /* normal job completion glink response */
+ NORMAL_RESPONSE = 0,
+ /* process updates poll memory instead of glink response */
+ POLL_MODE = 1,
+};
+
static const char *domains[FASTRPC_DEV_MAX] = { "adsp", "mdsp",
"sdsp", "cdsp", "cdsp1" };
struct fastrpc_phy_page {
@@ -258,6 +271,12 @@ struct fastrpc_invoke_ctx {
u64 *perf_dsp;
u64 ctxid;
u64 msg_sz;
+ /* Threads poll for specified timeout and fall back to glink wait */
+ u64 poll_timeout;
+ /* work done status flag */
+ bool is_work_done;
+ /* response flags from remote processor */
+ enum fastrpc_response_flags rsp_flags;
struct kref refcount;
struct list_head node; /* list of ctxs */
struct completion work;
@@ -682,6 +701,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
ctx->crc = (u32 *)(uintptr_t)inv2->crc;
ctx->perf_dsp = (u64 *)(uintptr_t)inv2->perf_dsp;
ctx->perf_kernel = (u64 *)(uintptr_t)inv2->perf_kernel;
+ ctx->poll_timeout = (u64)inv2->poll_timeout;
if (ctx->perf_kernel) {
ctx->perf = kzalloc(sizeof(*(ctx->perf)), GFP_KERNEL);
if (!ctx->perf)
@@ -692,6 +712,8 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
ctx->pid = current->pid;
ctx->tgid = user->tgid;
ctx->cctx = cctx;
+ ctx->rsp_flags = NORMAL_RESPONSE;
+ ctx->is_work_done = false;
init_completion(&ctx->work);
INIT_WORK(&ctx->put_work, fastrpc_context_put_wq);

@@ -1256,6 +1278,87 @@ static void fastrpc_update_invoke_count(u32 handle, u64 *perf_counter,
*count++;
}

+static int poll_for_remote_response(struct fastrpc_invoke_ctx *ctx, u64 timeout)
+{
+ int err = -EIO, i, j;
+ u32 sc = ctx->sc;
+ struct fastrpc_invoke_buf *list;
+ struct fastrpc_phy_page *pages;
+ u64 *fdlist = NULL;
+ u32 *crclist = NULL, *poll = NULL;
+ unsigned int inbufs, outbufs, handles;
+
+ /* calculate poll memory location */
+ inbufs = REMOTE_SCALARS_INBUFS(sc);
+ outbufs = REMOTE_SCALARS_OUTBUFS(sc);
+ handles = REMOTE_SCALARS_INHANDLES(sc) + REMOTE_SCALARS_OUTHANDLES(sc);
+ list = fastrpc_invoke_buf_start(ctx->rpra, ctx->nscalars);
+ pages = fastrpc_phy_page_start(list, ctx->nscalars);
+ fdlist = (u64 *)(pages + inbufs + outbufs + handles);
+ crclist = (u32 *)(fdlist + FASTRPC_MAX_FDLIST);
+ poll = (u32 *)(crclist + FASTRPC_MAX_CRCLIST);
+
+ /* poll on memory for DSP response. Return failure on timeout */
+ for (i = 0, j = 0; i < timeout; i++, j++) {
+ if (*poll == FASTRPC_POLL_RESPONSE) {
+ err = 0;
+ ctx->is_work_done = true;
+ ctx->retval = 0;
+ break;
+ }
+ if (j == FASTRPC_POLL_TIME_MEM_UPDATE) {
+ /* make sure that all poll memory writes by DSP are seen by CPU */
+ dma_rmb();
+ j = 0;
+ }
+ udelay(1);
+ }
+ return err;
+}
+
+static inline int fastrpc_wait_for_response(struct fastrpc_invoke_ctx *ctx,
+ u32 kernel)
+{
+ int err = 0;
+
+ if (kernel) {
+ if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
+ err = -ETIMEDOUT;
+ } else {
+ err = wait_for_completion_interruptible(&ctx->work);
+ }
+
+ return err;
+}
+
+static int fastrpc_wait_for_completion(struct fastrpc_invoke_ctx *ctx,
+ u32 kernel)
+{
+ int err;
+
+ do {
+ switch (ctx->rsp_flags) {
+ case NORMAL_RESPONSE:
+ err = fastrpc_wait_for_response(ctx, kernel);
+ if (err || ctx->is_work_done)
+ return err;
+ break;
+ case POLL_MODE:
+ err = poll_for_remote_response(ctx, ctx->poll_timeout);
+ /* If polling timed out, move to normal response mode */
+ if (err)
+ ctx->rsp_flags = NORMAL_RESPONSE;
+ break;
+ default:
+ err = -EBADR;
+ dev_dbg(ctx->fl->sctx->dev, "unsupported response type:0x%x\n", ctx->rsp_flags);
+ break;
+ }
+ } while (!ctx->is_work_done);
+
+ return err;
+}
+
static int fastrpc_internal_invoke(struct fastrpc_user *fl, u32 kernel, struct fastrpc_invoke_v2 *inv2)
{
struct fastrpc_invoke_ctx *ctx = NULL;
@@ -1301,16 +1404,22 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl, u32 kernel, struct
if (err)
goto bail;

- if (kernel) {
- if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
- err = -ETIMEDOUT;
- } else {
- err = wait_for_completion_interruptible(&ctx->work);
- }
+ if (ctx->poll_timeout != 0 && handle > FASTRPC_MAX_STATIC_HANDLE &&
+ fl->cctx->domain_id == CDSP_DOMAIN_ID &&
+ fl->pd == USER_PD)
+ ctx->rsp_flags = POLL_MODE;

+ err = fastrpc_wait_for_completion(ctx, kernel);
if (err)
goto bail;

+ if (!ctx->is_work_done) {
+ err = -ETIMEDOUT;
+ dev_dbg(fl->sctx->dev, "Invalid workdone state for handle 0x%x, sc 0x%x\n",
+ handle, sc);
+ goto bail;
+ }
+
/* make sure that all memory writes by DSP are seen by CPU */
dma_rmb();
PERF(ctx->perf_kernel, GET_COUNTER((u64 *)ctx->perf, PERF_PUTARGS),
@@ -2627,12 +2736,14 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
ctx = idr_find(&cctx->ctx_idr, ctxid);
spin_unlock_irqrestore(&cctx->lock, flags);

+ /* Ignore this failure as context returned will be NULL for polling mode */
if (!ctx) {
- dev_err(&rpdev->dev, "No context ID matches response\n");
- return -ENOENT;
+ dev_dbg(&rpdev->dev, "No context ID matches response\n");
+ return 0;
}

ctx->retval = rsp->retval;
+ ctx->is_work_done = true;
complete(&ctx->work);

/*
diff --git a/include/uapi/misc/fastrpc.h b/include/uapi/misc/fastrpc.h
index 1edc7c04b171..dde684554011 100644
--- a/include/uapi/misc/fastrpc.h
+++ b/include/uapi/misc/fastrpc.h
@@ -86,7 +86,8 @@ struct fastrpc_invoke_v2 {
__u64 crc;
__u64 perf_kernel;
__u64 perf_dsp;
- __u32 reserved[12];
+ __u64 poll_timeout;
+ __u32 reserved[10];
};

struct fastrpc_init_create {
--
2.34.1