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

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Message-Id: <200711132018.22995.david-b@pacbell.net>
Date:	Tue, 13 Nov 2007 20:18:22 -0800
From:	David Brownell <david-b@...bell.net>
To:	"eric miao" <eric.y.miao@...il.com>
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 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.

> +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.

> 
> -	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.

- Dave
-
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