On Thu, Jun 27, 2013 at 06:38:27PM -0700, Jeremy Chadwick wrote: > Next, this statement by ahci(4) then confuses the user: > > > ahci0: AHCI v1.30 with 6 6Gbps ports, Port Multiplier not supported > > You see, when AHCI was invented, the existing idea was that all ports > would have the same speed (and that was the case at the time). Only > somewhat recently have some vendors begun to mix-match speeds on the > same controller -- like this one. > > The AHCI specification probably (I have not read it even recently) only > provides a number indicating "the total number of ports" followed by a > single number indicating "the speed". > > There may be support somewhere within AHCI to provide an updated way to > get more granular information, but I do not know if that's the case. > > If there is, FreeBSD's ahci(4) driver does not support such at this > time (see sys/dev/ahci/ahci.c around line 502 for the device_printf() > call and what the arguments are (specifically AHCI_CAP_ISS and > AHCI_CAP_NPMASK)).
Just a technical follow-up: I spent some time this evening looking at AHCI specification 1.30. I'll try to explain the situation. First, at the HBA level (meaning the entire AHCI controller): Bits 23-30 of CAP (reg. offset 0x00): Interface Speed Support (ISS). This indicates, quote, "the maximum speed the HBA can support on its ports". Next, on a per-port basis, there are two registers available relating to speed: one indicates speed, the other controls/limits speed: 1) Bits 7-4 of PxSSTS (reg. offset 0x28): SPD: Port x Serial ATA Status (SCR0: SStatus). This indicates, quote, "the negotiated interface speed". 2) Bits 7-4 of PxSCTL (reg. offset 0x2c): SPD: Port x Serial ATA Control (SCR2: SControl). The register controls, quote, "the highest allowable speed of the interface". The bit definitions indicate a way to limit the speed of a port and do not indicate capability. The actual 1.30 specification even has a section (10.5) on this whole ordeal, which states clearly, quote: ==== 10.5 Interface Speed Support The HBA indicates the maximum speed it can support via the CAP.ISS register. Software can further limit the speed of a port by manipulating each port's PxSCTL.SPD field to a lower value. ==== AHCI spec "proposal" 1.31 also does not address/cover this (all that adds is per-port sleep capabilities). I will point out that SATA600 is not officially mentioned in any spec at this time (that I can get my hands on), so what all the OSes run off of are educated assumptions. :-) But theoretically, a newer AHCI spec could support per-port maximum speed indication. It's not easy to phrase all this tersely in a single device_printf(), and there has already been opposition to adding printing of more lines to the existing drivers/in dmesg (meaning, printing 6 lines, one for each port, indicating active speed + maximum speed, would probably be looked down upon outside of verbose booting). The best I can come up with is this: ahci0: AHCI v1.30, 6 ports, maximum 6Gbps, Port Multiplier not supported ...which is better, but could still be interpreted as "6 ports with a maximum of 6Gbps per port". Hope this sheds light in some way or another. -- | Jeremy Chadwick j...@koitsu.org | | UNIX Systems Administrator http://jdc.koitsu.org/ | | Making life hard for others since 1977. PGP 4BD6C0CB | _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
