From: David Miller <davem@davemloft.net>
To: pavel@ucw.cz
Cc: niklas.cassel@axis.com, peppe.cavallaro@st.com,
alexandre.torgue@st.com, Jose.Abreu@synopsys.com,
niklass@axis.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/4] net: stmmac: use correct barrier between coherent memory and MMIO
Date: Fri, 02 Mar 2018 09:54:11 -0500 (EST) [thread overview]
Message-ID: <20180302.095411.1270630534912987342.davem@davemloft.net> (raw)
In-Reply-To: <20180302091959.GC15948@amd>
From: Pavel Machek <pavel@ucw.cz>
Date: Fri, 2 Mar 2018 10:20:00 +0100
>> This barrier cannot be a simple dma_wmb(), since a dma_wmb() is only
>> used to guarantee the ordering, with respect to other writes,
>> to cache coherent DMA memory.
>
> Could you explain this a bit more (and perhaps in code comment)?
>
> Ensuring other writes are done before writing the "GO!" bit should be
> enough, no?
Indeed, the chip should never look at the descriptor contents unless
the GO bit is set.
If there are ways that it can, this must be explained and documented
since it is quite unusual compared to other hardware.
> (If it is not, do we need heavier barriers in other places, too?)
Right.
next prev parent reply other threads:[~2018-03-02 14:54 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-26 21:47 [PATCH net-next 0/4] stmmac barrier fixes and cleanup Niklas Cassel
2018-02-26 21:47 ` [PATCH net-next 1/4] net: stmmac: ensure that the MSS desc is the last desc to set the own bit Niklas Cassel
2018-02-26 21:47 ` [PATCH net-next 2/4] net: stmmac: use correct barrier between coherent memory and MMIO Niklas Cassel
2018-03-02 9:20 ` Pavel Machek
2018-03-02 14:54 ` David Miller [this message]
2018-03-02 23:28 ` Niklas Cassel
2018-03-07 15:32 ` David Miller
2018-03-07 17:21 ` Niklas Cassel
2018-03-07 17:42 ` David Miller
2018-03-07 18:09 ` Niklas Cassel
2018-03-08 9:05 ` Pavel Machek
2018-02-26 21:47 ` [PATCH net-next 3/4] net: stmmac: ensure that the device has released ownership before reading data Niklas Cassel
2018-02-26 21:47 ` [PATCH net-next 4/4] net: stmmac: make dwmac4_release_tx_desc() clear all descriptor fields Niklas Cassel
2018-02-27 19:28 ` [PATCH net-next 0/4] stmmac barrier fixes and cleanup David Miller
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