Re: Disabling Command Completion Coalescing (CCC) in SATA AHCI

[Sergei Shtylyov <sshtylyov@mvista.com>]

Hello.

On 20-05-2011 0:32, Pallav Bose wrote:

> I'm working on 2.6.35.9 version of the Linux kernel and am trying to
> disable Command Completion Coalescing. I have Native Command Queuing
> enabled by activating the RAID mode through the BIOS.

> I was looking at the Serial ATA AHCI 1.3 Specification and found on
> page 115 that -

> The CCC feature is only in use when CCC_CTL.EN is set to ‘1’. If
> CCC_CTL.EN is set to ‘0’, no CCC interrupts shall be generated.

> Next, I had a look at the relevant code (namely, the files concerning
> AHCI) for this version of the kernel but wasn't able to make any
> progress. I found the following enum constant - HOST_CAP_CCC = (1<<
> 7) - in drivers/ata/ahci.h, but I'm not sure how this should be
> modified to disable command coalescing. I did set HOST_CAP_CCC to 0
> but through some experiments that I conducted, I found that responses
> were being batched.

    This constant is only used to report the controller capability, I see no 
other code depending on it, hence there doesn't seem to be any CCC support...

[...]

> The mass storage controller in the system is: Promise Technology, Inc.
> PDC20268 (Ultra100 TX2) (rev 02),

    I don't understand. This controller is not AHCI, and not even SATA one.

> and the HDD being used is: WD Caviar Black (Model number - WD1001FALS).

WBR, Sergei