linux-kernel - Re: [PATCH] backlight: initialize struct backlight

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Message-Id: <20120522135902.90253d07.akpm@linux-foundation.org>
Date:	Tue, 22 May 2012 13:59:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Corentin Chary <corentin.chary@...il.com>
Cc:	Richard Purdie <rpurdie@...ys.net>,
	Keith Packard <keithp@...thp.com>,
	David Airlie <airlied@...ux.ie>,
	Matthew Garrett <mjg@...hat.com>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Mathieu Poirier <mathieu.poirier@...aro.org>,
	Dave Airlie <airlied@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Axel Lin <axel.lin@...il.com>, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
	linux-fbdev@...r.kernel.org, patches@...nsource.wolfsonmicro.com,
	linux-omap@...r.kernel.org
Subject: Re: [PATCH] backlight: initialize  struct backlight_properties
 properly

On Mon, 21 May 2012 09:24:35 +0200
Corentin Chary <corentin.chary@...il.com> wrote:

> In all these files, the .power field was never correctly initialized.
> 
> ...
>
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -342,6 +342,7 @@ int intel_panel_setup_backlight(struct drm_device *dev)
>  	else
>  		return -ENODEV;
>  
> +	memset(&props, 0, sizeof(props));

This code is all still quite fragile.  What happens if we add a new
field to backlight_properties?  We need to go edit a zillion drivers?

There are two ways of fixing this:

a) write and use

void backlight_properties_init(struct backlight_properties *props,
				int type, int max_brightness, etc);

   or

b) edit all sites to do

	struct backlight_properties bl_props = {
		.type = BACKLIGHT_RAW,
		.max_brighness = intel_panel_get_max_backlight(dev),
		.power = FB_BLANK_UNBLANK,
	};

they're largely equivalent - the struct will be zeroed out and
then certain fields will be initialised.  a) is a bit better because
some future field may not want the all-zeroes pattern (eg, a spinlock).

But they're both better than what we have now!
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