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

[Sergei Shtylyov]

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. :-(
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/