[SeaBIOS] [PATCH] mpt-scsi: Align MPT request to 8 bytes

Liran Alon liran.alon at oracle.com
Sat Dec 1 00:46:06 CET 2018

> On 30 Nov 2018, at 21:20, Kevin O'Connor <kevin at koconnor.net> wrote:
> On Wed, Nov 28, 2018 at 05:50:01PM +0200, Liran Alon wrote:
>> From: Nikita Leshchenko <nikita.leshchenko at oracle.com>
>> When mpt-scsi receives a SCSI message, it wraps it in a MPT request
>> message and writes it's address to an IO port to be added to the
>> request queue.
>> This MPT request is allocated on the stack. Previous to this commit,
>> the request is aligned to 4 bytes. However, VirtualBox LSI53c1030
>> device emulation aligns the request address to 8 bytes.
>> Therefore, this commit change alignment of request to 8 bytes.
>> VirtualBox source code which handles this is at
>> Devices/Storage/DevLsiLogicSCSI.cpp. lsilogicRegisterWrite()
>> LSILOGIC_REG_REQUEST_QUEUE handler adds the request to the
>> queue (pRequestQueueBase). lsilogicR3Worker() reads request from
>> pRequestQueueBase and aligns it to 8 bytes
>> (u32RequestMessageFrameDesc & ~0x07).
> Thanks.  Is this change done to match virtualbox, or because it fixes
> some type of problem?

It can be seen from QEMU’s mptsas_mmio_write() MPI_REQUEST_POST_FIFO_OFFSET handler
that QEMU aligns this value to 4 bytes which matches current SeaBIOS code.

However QEMU only emulates LSISAS1068 and not LSILOGIC53C1030.
This mpt-scsi.c SeaBIOS driver is suppose to handle both devices.

Therefore, we thought that maybe LSILOGIC53C1030 does requires value to be aligned to 8 bytes.
In contrast to LSISAS1068. Deduced from VirtualBox device emulation.


> -Kevin

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