linux-kernel - Re: [PATCH] leds: pm8058: Make ledtype pointer sized type

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Message-ID: <20171130221855.GW28761@minitux>
Date:   Thu, 30 Nov 2017 14:18:55 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: [PATCH] leds: pm8058: Make ledtype pointer sized type

On Thu 30 Nov 01:40 PST 2017, Pavel Machek wrote:

> On Wed 2017-11-29 19:05:43, Bjorn Andersson wrote:
> > The pointer returned by of_device_get_match_data() doesn't have the same
> > size as u32 on 64-bit architectures, causing issues when compile testing
> > the driver on such platform. Make ledtype unsigned long instead, to
> > solve this problem.
> > 
> > Fixes: 7f866986e705 ("leds: add PM8058 LEDs driver")
> > Cc: Linus Walleij <linus.walleij@...aro.org>
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> Ummm... no?
> 
> extern const void *of_device_get_match_data(const struct device *dev);
> 

Right, this returns a pointer, which is of architecture dependent size.

> 
> > diff --git a/drivers/leds/leds-pm8058.c b/drivers/leds/leds-pm8058.c
> > index a52674327857..cc2afe81720d 100644
> > --- a/drivers/leds/leds-pm8058.c
> > +++ b/drivers/leds/leds-pm8058.c
> > @@ -29,7 +29,7 @@
> >  struct pm8058_led {
> >  	struct regmap *map;
> >  	u32 reg;
> > -	u32 ledtype;
> > +	unsigned long ledtype;
> 
> Make it void *. u32 is buggy. unsigned long is merely ugly code. void
> * is not nice, but certainly better than unsigned long.
> 

unsigned long is the integer type in the kernel that has the same size
as a pointer, similar to the C-standard's intptr_t. So this is the
idiomatic way to pass an integer data type via a pointer variable in the
kernel.

Regards,
Bjorn