On 3/23/2018 12:43 PM, David Miller wrote:

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

quoted

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.

I can certainly update the commit text for this or spin into its own
patch to make it obvious.

	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!

It could if txdata->tx_db was not a union. There is a data dependency
between txdata->tx_db.data.prod and txdata->tx_db.raw. 

So, no reordering.

I can argue that barrier() here is useless in fact.

Anyhow, I'll spin this piece out of this patch so that we pay special
attention with a better description.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.