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Message-ID: <49295da9-82d4-45a0-a2a4-fdaa6600c70d@quicinc.com>
Date: Wed, 29 Jan 2025 11:12:16 +0530
From: Ekansh Gupta <quic_ekangupt@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: <srinivas.kandagatla@...aro.org>, <linux-arm-msm@...r.kernel.org>,
<gregkh@...uxfoundation.org>, <quic_bkumar@...cinc.com>,
<linux-kernel@...r.kernel.org>, <quic_chennak@...cinc.com>,
<dri-devel@...ts.freedesktop.org>, <arnd@...db.de>
Subject: Re: [PATCH v2 4/5] misc: fastrpc: Add polling mode support for
fastRPC driver
On 1/29/2025 4:59 AM, Dmitry Baryshkov wrote:
> 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?
This design is based on the implementation on DSP firmware as of today:
Call flow: https://github.com/quic-ekangupt/fastrpc/blob/invokev2/Docs/invoke_v2.md#5-polling-mode
Can you please give some reference to the async I/O protocol that you've
suggested? I can check if it can be implemented here.
--ekansh
>
>> Signed-off-by: Ekansh Gupta <quic_ekangupt@...cinc.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
>>
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