Re: [PATCH v11 4/4] misc: fastrpc: Add polling mode support for fastRPC driver

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Wed, May 20, 2026 at 12:20:47PM +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. This adds latency to overall fastrpc
> call as CPU wakeup and scheduling latencies are included. Add 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. In case
> poll timeout happens, the call will fallback to normal RPC mode.  Poll
> mode can be enabled by user by using FASTRPC_IOCTL_SET_OPTION ioctl
> request with FASTRPC_POLL_MODE request id.
> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/misc/fastrpc.c      | 167 ++++++++++++++++++++++++++++++++++--
>  include/uapi/misc/fastrpc.h |  29 +++++++
>  2 files changed, 189 insertions(+), 7 deletions(-)
> 
> @@ -1813,6 +1907,35 @@ static int fastrpc_get_info_from_kernel(struct fastrpc_ioctl_capability *cap,
>  	return 0;
>  }
>  
> +static int fastrpc_set_option(struct fastrpc_user *fl, char __user *argp)
> +{
> +	struct fastrpc_ioctl_set_option opt = {0};
> +	int i;
> +
> +	if (!fl->cctx->poll_mode_supported)
> +		return -EOPNOTSUPP;

This is being handled too early. What if the user passes any other
option?

> +
> +	if (copy_from_user(&opt, argp, sizeof(opt)))
> +		return -EFAULT;
> +
> +	for (i = 0; i < ARRAY_SIZE(opt.reserved); i++) {
> +		if (opt.reserved[i] != 0)
> +			return -EINVAL;
> +	}
> +
> +	if (opt.request_id != FASTRPC_POLL_MODE)
> +		return -EINVAL;
> +
> +	if (opt.value == FASTRPC_POLL_MODE_ENABLE)
> +		fl->poll_mode = true;
> +	else if (opt.value == FASTRPC_POLL_MODE_DISABLE)
> +		fl->poll_mode = false;
> +	else
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +

-- 
With best wishes
Dmitry