From: Stanislaw Gruszka <sgruszka@redhat.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Wey-Yi Guy <wey-yi.w.guy@intel.com>,
Intel Linux Wireless <ilw@linux.intel.com>,
linux-wireless@vger.kernel.org
Subject: Re: [RFC 3/4] iwlwifi: cleanup/fix memory barriers
Date: Tue, 7 Feb 2012 09:11:16 +0100 [thread overview]
Message-ID: <20120207081115.GC2246@redhat.com> (raw)
In-Reply-To: <4F2FFC25.8000705@sipsolutions.net>
On Mon, Feb 06, 2012 at 05:13:25PM +0100, Johannes Berg wrote:
> On 2/6/2012 5:09 PM, Stanislaw Gruszka wrote:
> >wmb(), rmb() are not needed when writel(), readl() are used as
> >accessors for MMIO. We use them indirectly via iowrite32(),
> >ioread32().
> >
> >What is needed mmiowb(), for synchronizing writes coming from
> >different CPUs on PCIe bridge (see in patch comments). This
> >fortunately is not needed on x86, where mmiowb() is just
> >defined as compiler barrier. As iwlwifi devices are most likely
> >not used on anything other than x86, this is not so important
> >fix.
>
> Technically, PCIe bridges can reorder writes as well, so we really
> need to do a dummy read somewhere -- we were discussing this
> internally recently as well.
PCIe can reorder writes only if they come from different CPUs,
good examples are in "LOCKS VS I/O ACCESSES" in
Documentation/memory-barriers.txt
Stanislaw
next prev parent reply other threads:[~2012-02-07 8:11 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-06 16:09 [RFC 1/4] iwlwifi: dump stack when fail to gain access to the device Stanislaw Gruszka
2012-02-06 16:08 ` wwguy
2012-02-07 8:01 ` Stanislaw Gruszka
2012-02-07 14:21 ` Guy, Wey-Yi
2012-02-08 10:52 ` Stanislaw Gruszka
2012-02-06 16:09 ` [RFC 2/4] iwlwifi: always check if got h/w access before write Stanislaw Gruszka
2012-02-06 16:13 ` wwguy
2012-02-07 8:05 ` Stanislaw Gruszka
2012-02-07 14:20 ` Guy, Wey-Yi
2012-02-06 16:09 ` [RFC 3/4] iwlwifi: cleanup/fix memory barriers Stanislaw Gruszka
2012-02-06 16:13 ` Johannes Berg
2012-02-07 8:11 ` Stanislaw Gruszka [this message]
2012-02-07 8:25 ` Johannes Berg
2012-02-06 16:09 ` [RFC 4/4] iwlwifi: use writeb,writel,readl directly Stanislaw Gruszka
2012-02-06 16:32 ` wwguy
2012-02-07 8:22 ` Stanislaw Gruszka
2012-02-07 14:22 ` Guy, Wey-Yi
2012-02-10 12:01 ` [RFC 1/4] iwlwifi: dump stack when fail to gain access to the device Stanislaw Gruszka
2012-02-23 10:14 ` Stanislaw Gruszka
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