linux-kernel - Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11 (PCI_MULTITHREAD

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Message-ID: <20070508225159.3442563f@gondolin.boeblingen.de.ibm.com>
Date:	Tue, 8 May 2007 22:51:59 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Adrian Bunk <bunk@...sta.de>, Greg K-H <greg@...ah.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11
 (PCI_MULTITHREAD_PROBE)

On Tue, 8 May 2007 13:01:21 -0700 (PDT),
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Instead of changing existign probe functionality to be asynchronous, we 
> could *add* a new and asynchronous part to it. For example, we could make 
> the rule for PCI - or other bus - devices be:
> 
>  - the bus will *first* call the "probe()" function synchronously.
> 
>  - after that one has completed, we will call "probe_async()" 
>    asynchronously at some point (it ie might be scheduled immediately 
>    after the "probe()" call, but delayed by some arbitrary issues like 
>    just already having too many asynchronous probes on-going or similar)

Hm. This would mean that probe() would be the decision "I want to use
this device", while probe_async() would be "setup my device, may take
some time"? Could work.

> So an unmodified driver would basically work exactly like it does now, but 
> if a driver is happy with being called asynchronously, it could just 
> change it's 
> 
> 	.probe = mydriver_probe
> 
> thing into a
> 
> 	.probe_async = mydriver_probe
> 
> and we can do that ona per-driver basis with that kind of really simple 
> one-liner change.

But probe would return int, while probe_async would return void? Two
liner :)

> 
> In fact, there is nothing wrong with having *both* a synchronous part, and 
> an async part:
> 
> 	.probe = mydriver_setup,
> 	.probe_async = mydriver_spin_up_and_probe_devices,
> 
> and it would do basic setup (including, for example, the fast enumeration 
> of whatever devices are connected) synchronously, but then do anything 
> more in the async part - and the async part would still be guaranteed that 
> the setup has been run by the time it is scheduled (but not really have 
> any other guarantees).

Looks like an idea.

I'll sleep on it, just too tired to make sense.
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