From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: David Laight <David.Laight@ACULAB.COM>,
"'Dylan Hung'" <dylan_hung@aspeedtech.com>,
Jakub Kicinski <kuba@kernel.org>, Joel Stanley <joel@jms.id.au>
Cc: BMC-SW <BMC-SW@aspeedtech.com>,
Po-Yu Chuang <ratbert@faraday-tech.com>,
linux-aspeed <linux-aspeed@lists.ozlabs.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
OpenBMC Maillist <openbmc@lists.ozlabs.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH] net: ftgmac100: Fix missing TX-poll issue
Date: Wed, 21 Oct 2020 09:05:34 +1100 [thread overview]
Message-ID: <7b44608bed9eccad80457cbfdfcca9043aae56f2.camel@kernel.crashing.org> (raw)
In-Reply-To: <f75555e09d47476a871669ffe017c4f8@AcuMS.aculab.com>
On Tue, 2020-10-20 at 13:15 +0000, David Laight wrote:
> That rather depends where the data is 'stuck'.
>
> An old sparc cpu would flush the cpu store buffer before the read.
> But a modern x86 cpu will satisfy the read from the store buffer
> for cached data.
>
> If the write is 'posted' on a PCI(e) bus then the read can't overtake it.
> But that is a memory access so shouldn't be to a PCI(e) address.
>
> Shouldn't dma_wb() actually force your 'cpu to dram' queue be flushed?
> In which case you need one after writing the ring descriptor and
> before the poke of the mac engine.
>
> The barrier before the descriptor write only needs to guarantee
> ordering of the writes - it can probably be a lighter barrier?
>
> It might be that your dma_wmb() needs to do a write+read of
> an uncached DRAM location in order to empty the cpu to dram queue.
This is a specific bug with how a specific IP block is hooked up in
those SOCs, I wouldn't bloat the global dma_wmb for that. The read back
in the driver with appropriate comment should be enough.
Cheers,
Ben.
next prev parent reply other threads:[~2020-10-20 22:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-19 7:39 [PATCH] net: ftgmac100: Fix missing TX-poll issue Dylan Hung
2020-10-19 8:57 ` Joel Stanley
2020-10-19 9:19 ` Dylan Hung
2020-10-19 19:00 ` Jakub Kicinski
2020-10-19 23:23 ` Benjamin Herrenschmidt
2020-10-20 2:57 ` Jakub Kicinski
2020-10-20 6:15 ` Benjamin Herrenschmidt
2020-10-20 17:24 ` Jakub Kicinski
2020-10-20 6:14 ` Dylan Hung
2020-10-20 13:15 ` David Laight
2020-10-20 22:05 ` Benjamin Herrenschmidt [this message]
2020-10-20 19:49 ` Arnd Bergmann
2020-10-20 22:10 ` Benjamin Herrenschmidt
2020-10-20 22:25 ` Andrew Jeffery
2020-10-23 13:08 ` Dylan Hung
2020-10-26 22:21 ` Benjamin Herrenschmidt
2020-10-27 2:18 ` Joel Stanley
2020-10-21 7:16 ` Arnd Bergmann
2020-10-21 12:11 ` Arnd Bergmann
2020-10-22 7:40 ` Benjamin Herrenschmidt
2020-10-23 8:39 ` Arnd Bergmann
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