Re: [PATCH] IDE Power Management, try 2

[Bartlomiej Zolnierkiewicz]

On 5 Jun 2003, Benjamin Herrenschmidt wrote:

> Ok, Here's the new one.
>
> However, I'm not completely happy with it yet. Bart, as you suggested, I

Yeah, I am not happy too.

> moved the state value to drive in order to keep a normal taskfile struct
> in rq->special. But that has a drawback: The request beeing re-fetched
> from the queue on each step, it goes through start_request for each of
> them. So I needed a way to know when is the "first pass" so I could
> initialize drive->pm_step properly. I don't want to initialize it
> prior to queuing the request as it would be racy. In fact, that pm_step
> is really a property of the request itself.
>
> I had to add yet another rq->flags bit for that, and I think that sucks

You don't have if you use additional, default pm_state (on == 0).
This sucks too, but a bit less.

> Also, currently, I'm not passing the "state" argument of the PM callback
> to the PM request. That argument would be needed if we ever wanted to
> distinguish between S1,S2,S3,S4.... For example, that could be used to
> skip the STANDBY pass on suspend-to-disk to avoid the disk spinning down
> and back up (suspend-to-disk is slow enough already ;)
>
> So I'm considering going back to putting some custom pm state structure
> in rq->special, but having this structure hold a taskfile structure as
> it's first entry so it is transparent to the taskfile interrupt
> handlers. It's not the prettiest thing, but unless we add more fields
> to struct request (which would be an option too since those PM requests
> could be used by _any_ block driver to implement proper power
> management).
>
> Jens, Bart, what do you think ? Should I add pm_step & pm_state to
> struct request ? Do the "extended taskfile structure" thing ? Or just
> keep things like they are in this new patch and forget about carrying
> the PM state value ?

I think extending struct request is the way to go,
pm_step & pm_state or even pointer to rq_pm_struct.

> I also added another rq->flags bit for requests forced at the head of
> the queue with ide_preempt. This is typically for sense requests done
> by ide-cd (though I also spotted a user in the tcq stuff). I need that
> to make sure that if such a request ever happens to be pushed in front
> of the current PM request (with the drive->blocked flag already set),
> we don't enter an endless loop, fetching that new request and dropping
> it right away because we only accept PM requests from the queue once
> the drive is suspended.

Jens, I think generic version of ide_do_drive_cmd() would be useful for
other block devices, what do you think?

Regards,
--
Bartlomiej