Re: [PATCH 0/10] megaraid_sas: Updates for scsi-misc

[Hannes Reinecke <hare@suse.de>]

On 10/10/2011 09:02 AM, Hannes Reinecke wrote:
> On 10/10/2011 02:56 AM, Douglas Gilbert wrote:
>> On 11-10-09 10:10 AM, James Bottomley wrote:
>>> On Sun, 2011-10-09 at 09:56 -0400, Douglas Gilbert wrote:
>>>> On 11-10-08 09:14 PM, adam radford wrote:
>>>>> James/Linux-scsi,
>>>>>
>>>>> The following patch series for megaraid_sas brings the driver up
>>>>> to v6.12-rc1:
>>>>>
>>>>> 1. Continue booting immediately if FW in FAULT at driver load
>>>>> time.
>>>>> 2. Increase default cmds per lun to 256.
>>>>> 3. Fix mismatch in megasas_reset_fusion() mutex lock-unlock.
>>>>> 4. Remove some un-necessary code.
>>>>> 5. Clear state change interrupts for Fusion/Invader.
>>>>> 6. Clear FUSION_IN_RESET before enabling interrupts.
>>>>> 7. Add support for MegaRAID 9360/9380 12GB/s controllers.
>>>>> 8. Add multiple MSI-X vector/multiple reply queue support.
>>>>> 9. Add driver workaround for PERC5/1068 kdump kernel panic.
>>>>> 10. Version and Changelog update.
>>>>
>>>> I haven't checked all SAS HBAs in Linux but of those that I
>>>> have checked only one doesn't support the SMP pass-through
>>>> in the bsg driver. And that HBA driver is megaraid_sas **.
>>>
>>> Technically the megaraid_sas isn't really a SAS HBA, it's a RAID one
>>> that just happens to have SAS/SATA disk attachments. None of the
>>> RAID
>>> HBA's (including the IBM power raid) expose a BSG interface or even
>>> attach properly to the in-kernel SAS interfaces.
>>
>> In JBOD mode MegaRaid SAS controllers are SAS HBAs
>> (marketing BS aside). Their firmware has the same
>> SMP pass-through as LSI's MPT SAS Fusion controllers.
>>
>> There is no reason why a MegaRaid controller user
>> couldn't place a SAS-2 expander in front of an array
>> of disks and make some disks available to a MegaRaid
>> volume. Other array disks could be used by other
>> machines and the different sets could be isolated
>> from each other with SAS-2 zoning. The problem then
>> would be that via a MegaRaid SAS controller a user
>> could not monitor or control that zoning. Seems a
>> bit wasteful to add a "real" SAS HBA just to get
>> that capability.
>>
> Yes, true. But that's the megaraid SAS design.
> It's actually the same with every other RAID controller.
> Everyone (well, every reasonably recent one) supports SAS, but
> virtually no-one exposes them as such.
>
> Problem here is that the RAID controller have invented
> their own command set to talk to the RAID firmware.
> Most RAID firmware have support for SCSI passthrough
> commands (that's how we managed to get rid of cciss :-)
> but virtually none of those have support for transport-specific
> passthrough commands.
>
Correction: megaraid_sas has.

It's got two command definitions:

#define MFI_CMD_SMP 0x7
#define MFI_CMD_STP 0x8

Which indeed look like they could've been used to implement the 
respective bsg interface.

Hmm.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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