Date: Sat, 3 May 2003 19:12:05 +0200 (MET DST)
From: Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       linux-kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: Reserving an ATA interface
In-Reply-To: <1051981168.4107.58.camel@gaston>
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On 3 May 2003, Benjamin Herrenschmidt wrote:

>
> > Yesterday I was thinking about:
> > - default arch hwifs, added/probed in ide_init_defult_hwifs() if no
> >   IDE PCI/PCI (depends on arch, should be IDE PCI?) support is compiled in
> > - PCI hwifs
> > - legacy hwifs probed in ide_setup()
> > - legacy hwifs probed after PCI
> > and about ide_register_hw() + initializing flag.
> >
> > What a mess... ordering issues can make you crazy.
>
> Yup, I'd suggest we think about re-writing all that stuff for 2.7 :)

Yes, only remaining question is how... :-)

> > > The simplest solution I have in mind is to add an hwif flag,
> > > called "hold" (or whatever better name you find). Drivers like
> > > ide/ppc/pmac.c would set this flag for the "hotswap" media bay
> > > interface, and not for others.
> >
> > This change is obviously correct and it doesn't have influence on
> > any existing code.
> >
> > > The only change to the core code would then be for ide_register_hw
> > > to 'skip' those when searching for an available slot, and to call
> > > init_hwif_data when (!hwif->present && !hwif->hold) to handle case 2
> > > where the iops & other hwif fields (mmio among others) need to be
> > > reset to initial/legacy state.
> >
> > Less safe change but also okay, as callers .
> > btw, Can't "ghost ides" be dealed inside ppc specific code?
> >      Do you know when interface is valid and when it is "ghost",
> >      and what other OS-es do in this case?
>
> Not re-using the slot for an interface with the "hold" bit won't
> affect anybody but setters of that bit, so we are ok. The act of
> calling init_hwif_data when !present && !hold is the one bringing
> a possible change of behaviour to existing code.
>
> However, who calls ide_register_hw() dynamically ? ide-cs and ?
> I don't think there would much harm in re-calling init_hwif_data
> at this point since hwif->present is not set, we _are_ re-using
> the hwif, wether it was previously initialized or not by somebody
> else. In this case, we really want to "clean" it, don't we ?

Yes.

> Right now, the only problem with re-initializing this way that
> I've found is with hotswap interfaces like ide-pmac, because
> they will have preset special MMIO ops etc... and that call
> would revert that pre-setting. That's exactly why such interfaces
> should set the "hold" bit to "reserve" the hwif slot. You see
> the point ? I don't think there are much drivers aroung playing
> with such tricks though.
>
> All I can do within ide pmac itself is set or not that "hold"
> bit for those interfaces. I just need to set it on the hotswap
> ones (wthr they have devices connected or not) that way they
> stay around "reserved" for when a device gets plugged. Other
> "fixed" interfaces will have hwif->present cleared automatically
> by the probe code, and thus will be "freed" for other uses, if
> they don't have any device attached.
> (Which is why that init_hwif_data is needed to reset their hwif
> to something good default, and not whatever ide pmac have set).
>
> In 2.5, I can be slightly smarted since I'm calling the probe
> myself and no longer rely on the automatic initial probe done
> by the IDE layer, like for PCI devices, so I can actually
> "clear" those "empty" interfaces myself after they are probed.
> But still, it makes sense to have this "hold" flag to let a
> hotswap interface reserve a slot, and it makes sense when the
> interface isn't held by anybody to "clean it up" before giving
> it to somebody else.

Fully agreed.

> The only problem I see right now is for a dynamic interface
> (like ide-cs) where the _controller_ itself is hotswap, so
> the hwif slot cannot be reserved in advance _and_ that interface
> needs special IOps (which is fortunately not the case of ide-cs)
>
> Such an interface can't really know what slot will be
> picked by ide_register_hw() and can't "prepare" the HWIF with
> special iops, so it won't be much harmed by the fact we are
> calling init_hwif_data, but still, we should ultimately think
> about splitting completely the fact of allocating an hwif slot,
> setting it up, and triggering a probe on it. Those are 3 different
> things that are currently mixed in bad ways. I don't beleive
> fixing that fits in the 2.6 timeframe though.

Yeah, to be done, probably 2.7 :\.
--
Bartlomiej

> Ben.

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