From: George Wilson <ltcgcw-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
To: James Bottomley <jejb-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Cc: Christophe Ricard
<christophe.ricard-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: Re: tpm: read burstcount from TPM_STS in one 32-bit transaction
Date: Tue, 1 Aug 2017 10:59:19 -0500 [thread overview]
Message-ID: <20170801155919.GA26008@us.ibm.com> (raw)
In-Reply-To: <1501004171.3689.25.camel-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
On Tue, Jul 25, 2017 at 10:36:11AM -0700, James Bottomley wrote:
> On Tue, 2017-07-25 at 15:04 +0200, Michal Suchánek wrote:
> > Hello,
> >
> > in commit 9754d45e9970 ("tpm: read burstcount from TPM_STS in one
> > 32-bit transaction") you change reading of two 8-bit values to one
> > 32bit read. This is obviously wrong wrt endianess unless the
> > underlying tpm_tis_read32 does endian conversion.
>
> Some of the bus read primitives do do endianness conversions. The
> problem is with the SPI attachment, which has unclear endianness. A
> standard PCI bus attachment uses ioread32() which automatically
> transforms from a little endian bus to the cpu endianness, however SPI
> is forced to transfer the bytes one at a time over the serial bus and
> then transform. The assumption seems to be that the TIS TPM is
> replying in little endian format when SPI connected.
>
> We can probably get the PPC people to confirm this, I believe they have
> a SPI attached TPM.
All the current OpenPOWER hardware designs I'm aware of have the TPM on
I2C. Trusted Computing support in OpenPOWER firmware depends on it
being on I2C.
>
> James
>
>
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prev parent reply other threads:[~2017-08-01 15:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-25 13:04 tpm: read burstcount from TPM_STS in one 32-bit transaction Michal Suchánek
2017-07-25 17:36 ` [tpmdd-devel] " James Bottomley
2017-07-25 18:17 ` Michal Suchánek
[not found] ` <20170725201758.230de968-6hIufAJW0g4CVLCxKZUutA@public.gmane.org>
2017-08-01 13:31 ` Jarkko Sakkinen
[not found] ` <1501004171.3689.25.camel-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-08-01 15:59 ` George Wilson [this message]
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