From: "Michal Suchánek" <msuchanek@suse.de>
To: James Bottomley <jejb@linux.vnet.ibm.com>
Cc: Christophe Ricard <christophe.ricard@gmail.com>,
linux-kernel@vger.kernel.org, tpmdd-devel@lists.sourceforge.net,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
apronin@chromium.org
Subject: Re: [tpmdd-devel] tpm: read burstcount from TPM_STS in one 32-bit transaction
Date: Tue, 25 Jul 2017 20:17:58 +0200 [thread overview]
Message-ID: <20170725201758.230de968@kitsune.suse.cz> (raw)
In-Reply-To: <1501004171.3689.25.camel@linux.vnet.ibm.com>
On Tue, 25 Jul 2017 10:36:11 -0700
James Bottomley <jejb@linux.vnet.ibm.com> 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.
>
Yes, that makes sense.
Thanks for clarification.
Michal
next prev parent reply other threads:[~2017-07-25 18:17 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 [this message]
[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
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