Messages in this thread | | | Subject | Re: [PATCH] Broadcom 8603 SAS/SATA driver, rough draft | From | James Bottomley <> | Date | Sun, 23 Sep 2007 18:05:23 -0500 |
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On Sun, 2007-09-23 at 00:04 -0400, Jeff Garzik wrote: > Rather than sitting on this for far too long, I wanted to go ahead and > get this out there. I heard some chips might be trickling out into > public hands.
The first thing to note is about the specs and the pre-production hardware: the Linux Foundation has mechanism to get both into the hands of interested developers; if you can point me to contacts, I can at least get the NDA documentation programme ball rolling.
> This is a bare bones Broadcom 8603 SAS+SATA driver, attempting to use > the vaunted libsas. Notes:
I wouldn't call it "vaunted" but it's been a fun project.
> * A quick glance at the FIXMEs will tell you obviously doesn't work.
The first thing I really noted is that SMP and STP protocol support is stubbed out ... you really can't do anything other than direct device connection without them.
> * The hardware is quite simple and straightforward and easy to program > in an efficient way: each SAS port has a command queue (DMA ring) and > a response queue (DMA ring). Or if in SATA mode, just a command > queue.
That's not such a bad way of doing it ... it pretty much mimics the wire protocol, which is simply frame in/frame out for SAS.
> * The SAS/SATA negotiation is largely out of our hands. The silicon > does its thing, and then tells us what type of device connected. We > are then expected to switch the port to either SAS mode or SATA mode, > accordingly. > > * There is no firmware or anything. Just DMA and register bitbanging. > We have plenty of low-level control. > > * The state of SAS/SATA integration is perpetually pathetic. Updates > in this area are likely. There's a rumor Brian King @ IBM may look > into this area too. > > * This driver pretty much completely lacks exception handling.
I also note there's a slight nomenclature issue which will trip up SAS people. All through the driver, you seem to use the word "port" to refer to a physical phy. the struct bs_port seems to actually be a phy descriptor ... unless there's some missing phy<->port setup logic that will be in the final driver? The trouble is that phys and ports are distinct (and not equivalent) objects in SAS.
> As an aside, I am also writing a driver for Marvell chips that behave > quite similarly to this chip. It seems the future of storage might look > like these Broadcom and Marvell SAS+SATA DMA ring interfaces, in the > volume marketspace at least.
If you have a contact here too, I can get the LF NDA and hardware programmes rolling.
James
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