linux-kernel - Re: [PATCH v6 10/17] firmware: arm_scmi: Make polling mode optional

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Date:   Wed, 28 Jul 2021 15:34:18 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
        etienne.carriere@...aro.org, vincent.guittot@...aro.org,
        souvik.chakravarty@....com, igor.skalkin@...nsynergy.com,
        peter.hilber@...nsynergy.com, alex.bennee@...aro.org,
        jean-philippe@...aro.org, mikhail.golubev@...nsynergy.com,
        anton.yakovlev@...nsynergy.com, Vasyl.Vavrychuk@...nsynergy.com,
        Sudeep Holla <sudeep.holla@....com>,
        Andriy.Tryshnivskyy@...nsynergy.com
Subject: Re: [PATCH v6 10/17] firmware: arm_scmi: Make polling mode optional

On Mon, Jul 12, 2021 at 03:18:26PM +0100, Cristian Marussi wrote:
> Add a check for the presence of .poll_done transport operation so that
> transports that do not need to support polling mode have no need to provide
> a dummy .poll_done callback either and polling mode can be disabled in the
> SCMI core for that tranport.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
>  drivers/firmware/arm_scmi/driver.c | 43 ++++++++++++++++++------------
>  1 file changed, 26 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index a952b6527b8a..4183d25c9289 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -777,25 +777,34 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
>  	}
>  
>  	if (xfer->hdr.poll_completion) {
> -		ktime_t stop = ktime_add_ns(ktime_get(), SCMI_MAX_POLL_TO_NS);
> -
> -		spin_until_cond(scmi_xfer_done_no_timeout(cinfo, xfer, stop));
> -
> -		if (ktime_before(ktime_get(), stop)) {
> -			unsigned long flags;
> -
> -			/*
> -			 * Do not fetch_response if an out-of-order delayed
> -			 * response is being processed.
> -			 */
> -			spin_lock_irqsave(&xfer->lock, flags);
> -			if (xfer->state == SCMI_XFER_SENT_OK) {
> -				info->desc->ops->fetch_response(cinfo, xfer);
> -				xfer->state = SCMI_XFER_RESP_OK;
> +		if (info->desc->ops->poll_done) {
> +			ktime_t stop = ktime_add_ns(ktime_get(),
> +						    SCMI_MAX_POLL_TO_NS);
> +
> +			spin_until_cond(scmi_xfer_done_no_timeout(cinfo, xfer,
> +								  stop));
> +
> +			if (ktime_before(ktime_get(), stop)) {
> +				unsigned long flags;
> +
> +				/*
> +				 * Do not fetch_response if an out-of-order delayed
> +				 * response is being processed.
> +				 */
> +				spin_lock_irqsave(&xfer->lock, flags);
> +				if (xfer->state == SCMI_XFER_SENT_OK) {
> +					info->desc->ops->fetch_response(cinfo,
> +									xfer);
> +					xfer->state = SCMI_XFER_RESP_OK;
> +				}
> +				spin_unlock_irqrestore(&xfer->lock, flags);
> +			} else {
> +				ret = -ETIMEDOUT;
>  			}
> -			spin_unlock_irqrestore(&xfer->lock, flags);
>  		} else {
> -			ret = -ETIMEDOUT;
> +			dev_warn_once(dev,
> +				      "Polling mode is not supported by transport.\n");
> +			ret = EINVAL;

Can't we just return this error as early as possible if the user isn't
expected to use polling with this transport ? That would simplify the patch
(as most of it is due to indentation which can go away) as you need not
check it later ?

-- 
Regards,
Sudeep