Re: [PATCH 1/3] Make the IDE DMA timeout modifiable

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Mark Lord wrote:

>>>>    The original question concerned specifically the DMA command 
>>>> timeout which is twice more than the usual one, WAIT_CMD (10 seconds)...

>>> When a drive is in standby, we don't send it anything special to wake 
>>> up.
>>> So even DMA commands have to have a long enough timeout to allow
>>> for spinning up.

>>    Yes, but why *twice* as long as the others?

> I would guess simply because DMA has to transfer up to 256 sectors of data,
> possibly with sector reallocations, in addition to waiting for the drive
> to spin up.  Other commands don't.

    What?! PIO commands don't have to do this as well? :-)

> At the time that was coded (?), I suspect that PIO READ/WRITE commands
> were fed data as it became available to/from the drive.  This may or may

    I don't see *any* difference with the DMA commands here -- the drive has 
always been free to assert and deassert DMARQ at its well.

> not still be the case, but it does imply that they don't need to hang
> around as long on the timeouts as do DMA commands (which have to wait
> for *everything* to be transferred).

    Ah, that makes sense -- during PIO interrupts happen a lot more often.
20 secs still seem to be too much.

> Cheers

MBR, Sergei

PS: Your mail server still keeps bouncing me off. :-(