Re: [PATCH] iommu/arm-smmu-v3: poll cmdq until it has space

[John Garry]

On 21/09/2021 12:43, Fernand Sieber wrote:
>   	do {

I didn't follow the full logic of this change yet ...

>   		llq->val = READ_ONCE(cmdq->q.llq.val);
> -		if (!queue_full(llq))
> +		if (!queue_has_space(llq, n))

But is the polarity really correct? That is, if we don't have space, 
then exit with success (the function to check for space).

>   			break;
>
> +		/*
> +		 * We must return here even if there's no space, because the producer
> +		 * having moved forward could mean that the last thread observing the
> +		 * SMMU progress has allocated space in the cmdq and moved on, leaving
> +		 * us in this waiting loop with no other thread updating
> +		 * llq->state->val.

what is llq->state->val?

> +		 */
> +		if (llq->prod != prod)
> +			return -EAGAIN;
> +
>   		ret = queue_poll(&qp);

Thanks,
John