From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
"Shaikh, Azhar" <azhar.shaikh@intel.com>,
"tpmdd-devel@lists.sourceforge.net"
<tpmdd-devel@lists.sourceforge.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>
Subject: Re: [PATCH v3] tpm: Enable CLKRUN protocol for Braswell systems
Date: Sat, 10 Jun 2017 14:06:56 +0300 [thread overview]
Message-ID: <20170610110656.hucthdwxfv3s6zz2@intel.com> (raw)
In-Reply-To: <20170608183920.GA7984@obsidianresearch.com>
On Thu, Jun 08, 2017 at 12:39:20PM -0600, Jason Gunthorpe wrote:
> On Thu, Jun 08, 2017 at 07:22:59PM +0100, Alan Cox wrote:
> > > > > + outb(0x80, 0xCC);
> > > > > +
> > > > > + /* Make sure the above write is completed */
> > > > > + wmb();
> > > >
> > > > Why the wmb(). It doesn't do what the comment says! Also this code is x86
> > > > specific
> > > >
> > > >
> > >
> > > Memory barrier to enforce the order so that the outb() is
> > > completed, which ensures that the LPC clocks are running before
> > > sending any TPM command.
> >
> > wmb() doesn't do that. It merely ensures that the write has been posted
> > to the fabric. If as I suspect your LPC bus implements outb() as a
> > non-posted write you don't need the wmb().
>
> I think the point here is to bootstrap the sleeping LPC bus clock
> before a TPM command is issued, presumably because the auto-wakeup circuit
> is busted or something.
>
> For that purpose all that should be required is strong ordering of the
> outb relative to the other TPM commands at the LPC interface FIFO. I
> also think the wmb is not needed because outb is already defined to be
> strongly in order with respect to writel/readl ?
>
> Jason
writel AFAIK guarantees by itself strong RW ordering.
/Jarkko
next prev parent reply other threads:[~2017-06-10 11:06 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-01 19:13 [PATCH] tpm: Enable CLKRUN protocol for Braswell systems Azhar Shaikh
2017-06-01 23:56 ` kbuild test robot
2017-06-02 2:04 ` [PATCH v2] " Azhar Shaikh
[not found] ` <1496369044-38234-1-git-send-email-azhar.shaikh-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-06-05 13:32 ` Jarkko Sakkinen
2017-06-05 18:42 ` Shaikh, Azhar
2017-06-06 17:13 ` Jarkko Sakkinen
2017-06-07 21:23 ` [PATCH v3] " Azhar Shaikh
2017-06-07 21:44 ` Alan Cox
2017-06-08 1:11 ` Shaikh, Azhar
2017-06-08 12:38 ` Jarkko Sakkinen
2017-06-08 18:22 ` Alan Cox
2017-06-08 18:39 ` Jason Gunthorpe
2017-06-08 18:50 ` Alan Cox
2017-06-08 19:27 ` Shaikh, Azhar
2017-06-10 11:06 ` Jarkko Sakkinen [this message]
2017-06-08 19:02 ` Shaikh, Azhar
2017-06-08 23:46 ` [PATCH v4] " Azhar Shaikh
2017-06-10 11:13 ` Jarkko Sakkinen
2017-06-10 16:35 ` Shaikh, Azhar
2017-06-12 7:50 ` Jarkko Sakkinen
2017-06-14 0:51 ` Shaikh, Azhar
2017-06-14 14:46 ` Jarkko Sakkinen
2017-06-14 17:17 ` Shaikh, Azhar
2017-06-14 19:39 ` Azhar Shaikh
2017-06-18 23:52 ` Jarkko Sakkinen
[not found] ` <1497829956.2552.10.camel-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2017-06-19 2:12 ` Shaikh, Azhar
2017-06-19 2:17 ` [PATCH v5] " Azhar Shaikh
2017-06-19 14:51 ` Jarkko Sakkinen
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