Re: [PATCH 6/9] nvme-apple: Add initial Apple SoC NVMe driver

[Keith Busch]

On Mon, Mar 21, 2022 at 05:50:46PM +0100, Sven Peter wrote:
> +static bool apple_nvme_poll_cq(struct apple_nvme_queue *q,
> +			       struct io_comp_batch *iob)
> +{
> +	bool found = false;
> +
> +	while (apple_nvme_cqe_pending(q)) {
> +		found = true;
> +
> +		/*
> +		 * load-load control dependency between phase and the rest of
> +		 * the cqe requires a full read memory barrier
> +		 */
> +		dma_rmb();
> +		apple_nvme_handle_cqe(q, iob, q->cq_head);
> +		apple_nvme_update_cq_head(q);
> +	}
> +
> +	if (found)
> +		writel_relaxed(q->cq_head, q->cq_db);

Doesn't a relaxed write mean that a subsequent write can bypass the previous?
If so, that sounds like it can corrupt the cq head.