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SubjectRE: [PATCH 2/2] drivers: ipmi: Modify max length of IPMB packet
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-----Original Message-----
From: Corey Minyard <tcminyard@gmail.com> On Behalf Of Corey Minyard
Sent: Tuesday, November 12, 2019 3:30 PM
To: Vijay Khemka <vijaykhemka@fb.com>
Cc: Arnd Bergmann <arnd@arndb.de>; Greg Kroah-Hartman <gregkh@linuxfoundation.org>; openipmi-developer@lists.sourceforge.net; linux-kernel@vger.kernel.org; cminyard@mvista.com; Asmaa Mnebhi <Asmaa@mellanox.com>; joel@jms.id.au; linux-aspeed@lists.ozlabs.org; Sai Dasari <sdasari@fb.com>
Subject: Re: [PATCH 2/2] drivers: ipmi: Modify max length of IPMB packet

On Tue, Nov 12, 2019 at 07:56:34PM +0000, Vijay Khemka wrote:
>
>
> On 11/12/19, 4:48 AM, "Corey Minyard" <tcminyard@gmail.com on behalf of minyard@acm.org> wrote:
>
> On Mon, Nov 11, 2019 at 06:36:10PM -0800, Vijay Khemka wrote:
> > As per IPMB specification, maximum packet size supported is 255,
> > modified Max length to 240 from 128 to accommodate more data.
>
> I couldn't find this in the IPMB specification.
>
> IIRC, the maximum on I2C is 32 byts, and table 6-9 in the IPMI spec,
> under "IPMB Output" states: The IPMB standard message length is
> specified as 32 bytes, maximum, including slave address.
>
> We are using IPMI OEM messages and our response size is around 150
> bytes For some of responses. That's why I had set it to 240 bytes.

Hmm. Well, that is a pretty significant violation of the spec, but there's nothing hard in the protocol that prohibits it, I guess.

If Asmaa is ok with this, I'm ok with it, too.

It doesn't bother me either. But I would like to do some experiment/testing first before validating it. I will get back to you. Vijay, how are you doing your testing?

-corey

>
> I'm not sure where 128 came from, but maybe it should be reduced to 31.
>
> -corey
>
> >
> > Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
> > ---
> > drivers/char/ipmi/ipmb_dev_int.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/ipmi/ipmb_dev_int.c b/drivers/char/ipmi/ipmb_dev_int.c
> > index 2419b9a928b2..7f9198bbce96 100644
> > --- a/drivers/char/ipmi/ipmb_dev_int.c
> > +++ b/drivers/char/ipmi/ipmb_dev_int.c
> > @@ -19,7 +19,7 @@
> > #include <linux/spinlock.h>
> > #include <linux/wait.h>
> >
> > -#define MAX_MSG_LEN 128
> > +#define MAX_MSG_LEN 240
> > #define IPMB_REQUEST_LEN_MIN 7
> > #define NETFN_RSP_BIT_MASK 0x4
> > #define REQUEST_QUEUE_MAX_LEN 256
> > --
> > 2.17.1
> >
>
>
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