On 3/23/2018 12:43 PM, David Miller wrote: > From: Sinan Kaya <ok...@codeaurora.org> > 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.
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.
