From: Sinan Kaya <redacted>
Date: Fri, 23 Mar 2018 12:31:12 -0400

Sorry, you got me confused now.

If you look at the code closer, you'll see this.

	wmb();

	txdata->tx_db.data.prod += nbd;
	barrier();

	DOORBELL(bp, txdata->cid, txdata->tx_db.raw);

and you also asked me to rename DOORBELL to DOORBELL_RELAXED() to make
it obvious that we have a relaxed operator inside the macro.

This still doesn't match the stated pattern.

	wmb();
	/* no other memory or I/O or IOMEM operation */
	writel();

There is a write to a producer index there and then no non-compiler
barrier or any kind before the writel().

So, in fact, it might really need that implicit writel() barrier here!