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 - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
