linux-kernel - Re: [patch 15/15] PNP: convert resource options to single linked list

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Message-ID: <4845DBBA.9010607@keyaccess.nl>
Date:	Wed, 04 Jun 2008 02:03:06 +0200
From:	Rene Herman <rene.herman@...access.nl>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Adam Belay <ambx1@....rr.com>,
	Adam M Belay <abelay@....edu>,
	Li Shaohua <shaohua.li@...el.com>,
	Matthieu Castet <castet.matthieu@...e.fr>,
	Thomas Renninger <trenn@...e.de>,
	Jaroslav Kysela <perex@...ex.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Takashi Iwai <tiwai@...e.de>
Subject: Re: [patch 15/15] PNP: convert resource options to single linked
 list

On 04-06-08 01:03, Bjorn Helgaas wrote:

> That's definitely backwards.  I reversed the sizes, so we'll have
> 8 bits for the priority byte (including compatibility/performance/
> robustness) and 16 bits for the dependent set number.  Actually,
> I made the priority field 12 bits so we'd have space to keep
> PNP_RES_PRIORITY_INVALID as a truly out-of-band value.

Sounds perfect.

>>> +	for (i = 0; i == 0 || i < dev->num_dependent_sets; i++) {
>>> +		ret = pnp_assign_resources(dev, i);
>>> +		if (ret == 0)
>>>  			return 0;
>> Eeeew. Perhaps:
>>
>> i = 0;
>> do {
>> 	ret = pnp_assign_resources(dev, i);
>> 	if (ret == 0)
>> 		return 0;
>> } while (++i < dev->num_dependent_sets);
> 
> Heh :-)  I vacillated on that one because I have a personal aversion
> to "do { ... } while ()", especially with a pre-increment.  How would
> you feel about this alternative?
> 
>         ret = pnp_assign_resources(dev, 0);
>         if (ret == 0)
>                 return 0;
> 
>         for (i = 1; i < dev->num_dependent_sets; i++) {
>                 ret = pnp_assign_resources(dev, i);
>                 if (ret == 0)
>                         return 0;
>         }

You could fix the pre-increment by sticking a i++ inside the loop body 
but there's no arguing with personal aversions...

Yes, I think the latter is better. Straight-forward and clear.

>> Why do you do 0x800, 0x400 in that order? Shouldn't it just be 0x400, 
>> 0x800 to mimick the old order?
> 
> I think they do end up in the correct order because I'm passing the
> same list_head to both list_add() calls, e.g., we'll have something
> like this:
> 
>     io -> ...
>     io -> (io + 0x800) -> ...
>     io -> (io + 0x400) -> (io + 0x800) -> ...

Yep. Just needed to see it happen once in the quirk testing I just now did.

> I need to go back over all your comments and make sure I've addressed
> them all, then I'll post the revised patches, hopefully tomorrow.
> 
> Thanks again for all your work reviewing and testing these.  It's
> been incredibly useful.

I've been impressed by this work. This is a good redesign of PnP with a 
fully bisectable way to get there. And PnP was in need of some work...

Rene.
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