Re: [PATCH] Configure IDE probe delays

Jeff Garzik
2004-07-31T00:54:54Z

Alan Cox wrote:
> On Gwe, 2004-07-30 at 20:11, Todd Poynor wrote:
>
>>IDE initialization and probing makes numerous calls to sleep for 50
>>milliseconds while waiting for the interface to return probe status and
>>such.
>
>
> Please make it taint the kernel if you do that so we can ignore all the
> bug reports. That or justify it with a cite from the ATA standards ?

The 50 milliseconds is a pragmatic number you won't find in any
standard. Linux IDE driver does the "bang at the door" method of
probing, which you won't find in any standard either :)

The ATA standard defines times for things like software reset (SRST),
but Linux IDE driver takes a unique approach -- just issue down the
first command (IDENTIFY DEVICE), and see what you get. The command (or
error) responses give you information that allows you to probe further.

The 50ms delay hides things like the device coming out of reset, the
interface powering up on the first command issued to the device, etc.

IMO the number is a "change it at your own risk" number that shouldn't
be touched unless the touch-er is also willing to rewrite the IDE
driver's probe code ;-)

SATA is much faster at probing, and PATA will become progressively less
common, so the motivation for changing the probe code is low, too.

Jeff