linux-kernel - Re: [PATCH] hpsa: SCSI driver for HP Smart Array controllers

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Message-ID: <da824cf30903061355m4e5368b0q938776cf5d61a46a@mail.gmail.com>
Date:	Fri, 6 Mar 2009 13:55:13 -0800
From:	Grant Grundler <grundler@...gle.com>
To:	scameron@...rdog.cca.cpqcorp.net
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, mike.miller@...com,
	akpm@...ux-foundation.org, linux-scsi@...r.kernel.org,
	coldwell@...hat.com, hare@...ell.com, iss_storagedev@...com
Subject: Re: [PATCH] hpsa: SCSI driver for HP Smart Array controllers

On Fri, Mar 6, 2009 at 1:18 PM,  <scameron@...rdog.cca.cpqcorp.net> wrote:
> On Fri, Mar 06, 2009 at 12:59:48PM -0800, Grant Grundler wrote:
>> On Fri, Mar 6, 2009 at 6:38 AM,  <scameron@...rdog.cca.cpqcorp.net> wrote:
>> ...
>> > The command buffers have to be in the first 4GB of memory, as the command
>> > register is only 32 bits, so they are allocated by pci_alloc_consistent.
>>
>> Huh?!!
>> ISTR the mpt2sas driver is indicating it can handle 64-bit DMA masks for
>> both streaming and control data. I need to double check to be sure of that.
>
> it is something specific to smart array.  The command register that we
> stuff the bus address of the command into is only 32 bits wide.  Everything
> else it does is 64 bits.

Sorry...I'm spacing out and confusing my drivers.

thanks,
grant

>>
>> > However, the chained SG lists don't have that limitation, so I think they
>> > can be kmalloc'ed, and so not chew up and unreasonable amount of the
>> > pci_alloc_consistent memory and get a larger number of SGs.   ...right?
>> > Maybe that's the better way to do it.
>>
>> I thought the driver was tracking this and using the appropriate construct
>> based on which DMA mask is in effect.
>
> The DMA mask is insufficiently expressive to describe the limitations and
> capabilities of the Smart array.  There's no way to describe with a single
> DMA mask that the command register is 32-bits, but everything else is 64
> bits.
>
> -- steve
>
>
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