On Mon, Jan 27, 2025 at 10:12:38AM +0530, Ekansh Gupta wrote:
> 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.
Is there a chance to implement actual async I/O protocol with the help
of the poll() call instead of hiding the polling / wait inside the
invoke2?
>
> Signed-off-by: Ekansh Gupta <quic_ekang...@quicinc.com>
> ---
> drivers/misc/fastrpc.c | 122 +++++++++++++++++++++++++++++++++---
> include/uapi/misc/fastrpc.h | 3 +-
> 2 files changed, 114 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index cfacee0dded5..257a741af115 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -19,6 +19,7 @@
> #include <linux/rpmsg.h>
> #include <linux/scatterlist.h>
> #include <linux/slab.h>
> +#include <linux/delay.h>
> #include <linux/firmware/qcom/qcom_scm.h>
> #include <uapi/misc/fastrpc.h>
> #include <linux/of_reserved_mem.h>
> @@ -38,6 +39,7 @@
> #define FASTRPC_CTX_MAX (256)
> #define FASTRPC_INIT_HANDLE 1
> #define FASTRPC_DSP_UTILITIES_HANDLE 2
> +#define FASTRPC_MAX_STATIC_HANDLE (20)
> #define FASTRPC_CTXID_MASK (0xFF0)
> #define INIT_FILELEN_MAX (2 * 1024 * 1024)
> #define INIT_FILE_NAMELEN_MAX (128)
> @@ -106,6 +108,19 @@
>
> #define miscdev_to_fdevice(d) container_of(d, struct fastrpc_device, miscdev)
>
> +/* 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 {
> @@ -238,9 +253,16 @@ struct fastrpc_invoke_ctx {
> u32 sc;
> u64 *fdlist;
> u32 *crclist;
> + u32 *poll;
> void __user *crc;
> 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;
> @@ -258,6 +280,7 @@ struct fastrpc_invoke_ctx {
> struct fastrpc_ctx_args {
> struct fastrpc_invoke_args *args;
> void __user *crc;
> + u64 poll_timeout;
> };
>
> struct fastrpc_session_ctx {
> @@ -619,11 +642,14 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
> fastrpc_channel_ctx_get(cctx);
>
> ctx->crc = cargs->crc;
> + ctx->poll_timeout = cargs->poll_timeout;
> ctx->sc = sc;
> ctx->retval = -1;
> ctx->pid = current->pid;
> ctx->client_id = user->client_id;
> 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);
>
> @@ -882,7 +908,8 @@ static int fastrpc_get_meta_size(struct
> fastrpc_invoke_ctx *ctx)
> sizeof(struct fastrpc_invoke_buf) +
> sizeof(struct fastrpc_phy_page)) * ctx->nscalars +
> sizeof(u64) * FASTRPC_MAX_FDLIST +
> - sizeof(u32) * FASTRPC_MAX_CRCLIST;
> + sizeof(u32) * FASTRPC_MAX_CRCLIST +
> + sizeof(u32);
>
> return size;
> }
> @@ -975,6 +1002,8 @@ static int fastrpc_get_args(u32 kernel, struct
> fastrpc_invoke_ctx *ctx)
> pages = fastrpc_phy_page_start(list, ctx->nscalars);
> ctx->fdlist = (u64 *)(pages + ctx->nscalars);
> ctx->crclist = (u32 *)(ctx->fdlist + FASTRPC_MAX_FDLIST);
> + ctx->poll = (u32 *)(ctx->crclist + FASTRPC_MAX_CRCLIST);
> +
> args = (uintptr_t)ctx->buf->virt + metalen;
> rlen = pkt_size - metalen;
> ctx->rpra = rpra;
> @@ -1145,6 +1174,72 @@ static int fastrpc_invoke_send(struct
> fastrpc_session_ctx *sctx,
>
> }
>
> +static int poll_for_remote_response(struct fastrpc_invoke_ctx *ctx, u64
> timeout)
> +{
> + int err = -EIO, i, j;
> +
> + /* poll on memory for DSP response. Return failure on timeout */
> + for (i = 0, j = 0; i < timeout; i++, j++) {
> + if (*ctx->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,
> u32 handle, u32 sc,
> struct fastrpc_ctx_args *cargs)
> @@ -1180,16 +1275,20 @@ static int fastrpc_internal_invoke(struct
> fastrpc_user *fl, u32 kernel,
> 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->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();
> /* populate all the output buffers with results */
> @@ -1769,7 +1868,7 @@ static int fastrpc_invokev2(struct fastrpc_user *fl,
> char __user *argp)
> return -EFAULT;
>
> /* Check if all reserved fields are zero */
> - for (i = 0; i < 16; i++) {
> + for (i = 0; i < 14; i++) {
> if (inv2.reserved[i] != 0)
> return -EINVAL;
> }
> @@ -1779,6 +1878,7 @@ static int fastrpc_invokev2(struct fastrpc_user *fl,
> char __user *argp)
> return -ENOMEM;
>
> cargs->crc = (void __user *)(uintptr_t)inv2.crc;
> + cargs->poll_timeout = inv2.poll_timeout;
>
> err = fastrpc_remote_invoke(fl, &inv2.inv, cargs);
> kfree(cargs);
> @@ -2581,12 +2681,14 @@ 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 406b80555d41..1920c537bbbf 100644
> --- a/include/uapi/misc/fastrpc.h
> +++ b/include/uapi/misc/fastrpc.h
> @@ -84,7 +84,8 @@ struct fastrpc_invoke {
> struct fastrpc_invoke_v2 {
> struct fastrpc_invoke inv;
> __u64 crc;
> - __u32 reserved[16];
> + __u64 poll_timeout;
> + __u32 reserved[14];
> };
>
> struct fastrpc_init_create {
> --
> 2.34.1
>
--
With best wishes
Dmitry
