linux-kernel - Re: [PATCH] leds: lp55xx: make various arrays static const

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Message-ID: <20170629204831.GA763@amd>
Date:   Thu, 29 Jun 2017 22:48:31 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Colin King <colin.king@...onical.com>,
        Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: lp55xx: make various arrays static const

Hi!

> Thanks for the patch.
> 
> Do you have some profiling results showing the benefit of these changes?
> It seems that these functions are called only on driver initialization.
> Making the local arrays static will prevent releasing this memory even
> though it will be no longer needed.
> 
> Anyway, the size of arrays is 3 bytes, so the impact of these changes
> seems to be virtually negligible. I am not taking this patch unless
> you are able to provide the numbers showing the gain.

C will have to initialize the array on stack, then copy values
there.. which is ugly. "static const" also tells the reader what is
going on there (nothing).

I'd say this is a good patch.

Acked-by: Pavel Machek <pavel@....cz>

								Pavel

> > +++ b/drivers/leds/leds-lp5523.c
> > @@ -168,13 +168,13 @@ static int lp5523_post_init_device(struct lp55xx_chip *chip)
> >  static void lp5523_load_engine(struct lp55xx_chip *chip)
> >  {
> >  	enum lp55xx_engine_index idx = chip->engine_idx;
> > -	u8 mask[] = {
> > +	static const u8 mask[] = {
> >  		[LP55XX_ENGINE_1] = LP5523_MODE_ENG1_M,
> >  		[LP55XX_ENGINE_2] = LP5523_MODE_ENG2_M,
> >  		[LP55XX_ENGINE_3] = LP5523_MODE_ENG3_M,
> >  	};
> >  
> > -	u8 val[] = {
> > +	static const u8 val[] = {
> >  		[LP55XX_ENGINE_1] = LP5523_LOAD_ENG1,
> >  		[LP55XX_ENGINE_2] = LP5523_LOAD_ENG2,
> >  		[LP55XX_ENGINE_3] = LP5523_LOAD_ENG3,
> > @@ -188,7 +188,7 @@ static void lp5523_load_engine(struct lp55xx_chip *chip)
> >  static void lp5523_load_engine_and_select_page(struct lp55xx_chip *chip)
> >  {
> >  	enum lp55xx_engine_index idx = chip->engine_idx;
> > -	u8 page_sel[] = {
> > +	static const u8 page_sel[] = {
> >  		[LP55XX_ENGINE_1] = LP5523_PAGE_ENG1,
> >  		[LP55XX_ENGINE_2] = LP5523_PAGE_ENG2,
> >  		[LP55XX_ENGINE_3] = LP5523_PAGE_ENG3,
> > @@ -208,7 +208,7 @@ static void lp5523_stop_all_engines(struct lp55xx_chip *chip)
> >  static void lp5523_stop_engine(struct lp55xx_chip *chip)
> >  {
> >  	enum lp55xx_engine_index idx = chip->engine_idx;
> > -	u8 mask[] = {
> > +	static const u8 mask[] = {
> >  		[LP55XX_ENGINE_1] = LP5523_MODE_ENG1_M,
> >  		[LP55XX_ENGINE_2] = LP5523_MODE_ENG2_M,
> >  		[LP55XX_ENGINE_3] = LP5523_MODE_ENG3_M,
> > @@ -505,7 +505,7 @@ static int lp5523_load_mux(struct lp55xx_chip *chip, u16 mux, int nr)
> >  {
> >  	struct lp55xx_engine *engine = &chip->engines[nr - 1];
> >  	int ret;
> > -	u8 mux_page[] = {
> > +	static const u8 mux_page[] = {
> >  		[LP55XX_ENGINE_1] = LP5523_PAGE_MUX1,
> >  		[LP55XX_ENGINE_2] = LP5523_PAGE_MUX2,
> >  		[LP55XX_ENGINE_3] = LP5523_PAGE_MUX3,
> > 

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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