Re: [PATCH v8 4/4] misc: fastrpc: Add polling mode support for fastRPC driver

[Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>]

On 16-04-2026 16:25, Dmitry Baryshkov wrote:
> On Wed, Apr 15, 2026 at 04:55:30PM +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      | 137 ++++++++++++++++++++++++++++++++++--
>>  include/uapi/misc/fastrpc.h |  25 +++++++
>>  2 files changed, 155 insertions(+), 7 deletions(-)
>>
>> @@ -1813,6 +1908,30 @@ 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 (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)
>> +		fl->poll_mode = true;
> 
> This will enable poll mode on the platforms where it is not supported,
> later silinently changing back to the normal mode. Please don't surprise
> users and make this call fail if polling mode is not supported.
Ack. Working on adding compatible based checks for supporting platforms
by reading the root compatible string, something like pdmapper[1].

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/soc/qcom/qcom_pd_mapper.c#n643

Thanks,
Ekansh

> 
>> +	else
>> +		fl->poll_mode = false;
>> +
>> +	return 0;
>> +}
>> +
>