From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "Tyrel Datwyler" <tyreld@linux.vnet.ibm.com>,
"Michal Suchánek" <msuchanek@suse.de>,
"Ashley Lai" <ashleydlai@gmail.com>,
"Paul Mackerras" <paulus@samba.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Peter Huewe" <peterhuewe@gmx.de>,
"Marcel Selhorst" <tpmdd@selhorst.net>,
"Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>,
"Jason Gunthorpe" <jgunthorpe@obsidianresearch.com>,
tpmdd-devel@lists.sourceforge.net, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org
Subject: Re: ibmvtpm byteswapping inconsistency
Date: Sat, 28 Jan 2017 15:28:23 +1100 [thread overview]
Message-ID: <1485577703.2980.104.camel@kernel.crashing.org> (raw)
In-Reply-To: <48dc15a0-eaba-29e4-f39e-500177f98638@linux.vnet.ibm.com>
On Fri, 2017-01-27 at 12:32 -0800, Tyrel Datwyler wrote:
> Its possible being the end of the week I'm just a little dense, but
> wouldn't be64_to_cpu() imply that we are byte-swapping something that is
> already, or supposedly already, in BE format to cpu endianness? Which on
> a BE cpu I would expect a no-op, and on a LE cpu the 64bit word to have
> been swapped from BE --> LE?
It's in BE format in memory. In LE mode, loading it into a register will
get it the wrong way around, thus we have to swap it again. Once in a
register it has no "endianness" per-se, what matters is that the act
of loading from memory to a register would have loaded it the wrong
way around in LE.
> In my eyes the code does seem to support what I've argued. The same
> thing is done in the scsi VIO drivers. The CRQ structure is laid out and
> annotated BE. We use cpu_to_be() calls to load any non 8bit field.
> Finally, each word is swapped to cpu endian when we hand it off for the
> hcall.
>
> from ibmvfc_send_event():
>
> __be64 *crq_as_u64 = (__be64 *) &evt->crq;
>
> <..snip..>
>
> if ((rc = ibmvfc_send_crq(vhost, be64_to_cpu(crq_as_u64[0]),
> be64_to_cpu(crq_as_u64[1])))) {
>
> Again, maybe I'm missing something.
next prev parent reply other threads:[~2017-01-28 4:29 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-26 20:22 ibmvtpm byteswapping inconsistency Michal Suchánek
2017-01-26 22:05 ` Jason Gunthorpe
2017-01-26 22:43 ` Michal Suchanek
2017-01-26 22:58 ` Ashley Lai
2017-02-02 4:40 ` Vicky
2017-02-02 10:55 ` Michael Ellerman
2017-02-02 11:29 ` Michal Suchánek
2017-02-02 15:17 ` David Laight
2017-01-27 1:42 ` Tyrel Datwyler
2017-01-27 1:50 ` Benjamin Herrenschmidt
2017-01-27 9:03 ` Michal Suchanek
2017-01-27 21:19 ` Tyrel Datwyler
2017-01-30 4:32 ` Michael Ellerman
2017-01-30 20:34 ` Tyrel Datwyler
2017-01-31 8:38 ` Michael Ellerman
2017-01-27 18:02 ` Tyrel Datwyler
2017-01-27 19:58 ` Benjamin Herrenschmidt
2017-01-27 20:32 ` Tyrel Datwyler
2017-01-28 0:35 ` msuchanek
2017-01-28 4:28 ` Benjamin Herrenschmidt [this message]
2017-01-30 14:42 ` David Laight
2017-01-27 11:18 ` David Laight
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