linux-kernel - Re: [patch/rfc 1/4] GPIO implementation framework

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Message-ID: <f17812d70711132246i5e29600cqe96a2f51051a6f8f@mail.gmail.com>
Date:	Wed, 14 Nov 2007 14:46:27 +0800
From:	"eric miao" <eric.y.miao@...il.com>
To:	"David Brownell" <david-b@...bell.net>
Cc:	"Linux Kernel list" <linux-kernel@...r.kernel.org>,
	"Felipe Balbi" <felipebalbi@...rs.sourceforge.net>,
	"Bill Gatliff" <bgat@...lgatliff.com>,
	"Haavard Skinnemoen" <hskinnemoen@...el.com>,
	"Andrew Victor" <andrew@...people.com>,
	"Tony Lindgren" <tony@...mide.com>,
	"Jean Delvare" <khali@...ux-fr.org>,
	"Kevin Hilman" <khilman@...sta.com>,
	"Paul Mundt" <lethal@...ux-sh.org>,
	"Ben Dooks" <ben@...nity.fluff.org>
Subject: Re: [patch/rfc 1/4] GPIO implementation framework

On Nov 14, 2007 12:18 PM, David Brownell <david-b@...bell.net> wrote:
> On Tuesday 13 November 2007, eric miao wrote:
> > Here comes the point of "struct gpio_desc"
> >
> > Subject: [PATCH 3/5] use a per GPIO "struct gpio_desc" and chain
> > "gpio_chip" to a list
>
> I see what it does, but don't see the "why" ... surely
> you can come up with a one sentence description of why
> this would be better?
>
> And I'd been so glad to *get rid of* that list, too.

I'll be happy too.

>
>
> > +struct gpio_desc {
> > +     struct gpio_chip *chip;
> > +};
> > +
>
> > -/* gpio_lock protects modification to the table of chips and to
> > - * gpio_chip->requested.  If a gpio is requested, its gpio_chip
> > - * is not removable.
> > - */
>
> But it still protects data.  Don't remove documentation for
> what locks protect ... update it!  Otherwise someonels going
> to come by and make a change which breaks the locking model.
> Usually in some subtle (hard-to-debug) way.

I'd prefer to name it "gpio_desc_lock" instead, which is self-explanatory
and thus requires no comment at all

>
> >
> > -     for (id = 0; id < ARRAY_SIZE(chips); id++) {
> > -             chip = chips[id];
> > -             if (!chip)
> > -                     continue;
> > -
> > +     list_for_each_entry(chip, &gpio_chip_list, node) {
> >               seq_printf(s, "%sGPIOs %d-%d, %s%s:\n",
> >                               started ? "\n" : "",
> >                               chip->base, chip->base + chip->ngpio - 1,
>
> Note that this now produces the debug info in a relatively
> random order ... ordered by registration rather than anything
> useful, and hence awkward to read.
>
> It'd be better if you just scanned your new gpio_desc[]
> table in numeric order, and start a new section whenever
> you find a new gpio_chip.
>
> That'd get rid of that otherwise-useless list, too.
>

absolutely, you get the same feeling of mine and since this is for illustration
purpose only, I don't want more patches to fix this...

> - Dave
>



-- 
Cheers
- eric
-
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