From: Grant Likely <grant.likely@secretlab.ca>
To: Alexandre Courbot <acourbot@nvidia.com>,
Linus Walleij <linus.walleij@linaro.org>
Cc: linux-arch <linux-arch@vger.kernel.org>,
Alexandre Courbot <gnurou@gmail.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Arnd Bergmann <arnd@arndb.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 6/9] gpiolib: use descriptors internally
Date: Sat, 09 Feb 2013 09:17:29 +0000 [thread overview]
Message-ID: <20130209091729.978C73E1A18@localhost> (raw)
In-Reply-To: <CAAVeFu+phNtzzj7rw96g9iH8sj9gGqd5SfAqtkDHvu3PeL_oQA@mail.gmail.com>
On Thu, 7 Feb 2013 15:57:32 +0900, Alexandre Courbot <acourbot@nvidia.com> wrote:
> On Wed, Feb 6, 2013 at 2:53 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Sat, Feb 2, 2013 at 5:29 PM, Alexandre Courbot <acourbot@nvidia.com> wrote:
> >> +/**
> >> + * Convert a GPIO number to its descriptor
> >> + */
> >> +static struct gpio_desc *gpio_to_desc(unsigned gpio)
> >> +{
> >> + if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))
> >> + return NULL;
> >
> > Don't we want to return ERR_PTR(-EINVAL); here?
> >
> > Then you can use IS_ERR() on the pointers later.
> >
> > This is the approach taken by the external API for clk
> > and pins.
>
> Yes, that completely makes sense.
>
No, it does not. The ERR_PTR()/IS_ERR() is a horrible pattern for code
readability because it breaks the expectations that programmers have for
what is and is not a bad pointer. There are decades of history where the
test for a bad pointer is 'if (!ptr)'. Not only does ERR_PTR make make
that test not work, but the compiler won't tell you when you get it
wrong.
There are places where ERR_PTR makes sense. Particularly when
communicating with userspace where error codes have very specific
meanings, but I don't want it in the GPIO subsystem.
g.
WARNING: multiple messages have this Message-ID (diff)
From: Grant Likely <grant.likely@secretlab.ca>
To: Alexandre Courbot <acourbot@nvidia.com>,
Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
linux-arch <linux-arch@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Alexandre Courbot <gnurou@gmail.com>
Subject: Re: [PATCH 6/9] gpiolib: use descriptors internally
Date: Sat, 09 Feb 2013 09:17:29 +0000 [thread overview]
Message-ID: <20130209091729.978C73E1A18@localhost> (raw)
Message-ID: <20130209091729.Db6wM0tM4wj96rMV7sv4HLTSwBxtrK54kAGXMMxQ4GQ@z> (raw)
In-Reply-To: <CAAVeFu+phNtzzj7rw96g9iH8sj9gGqd5SfAqtkDHvu3PeL_oQA@mail.gmail.com>
On Thu, 7 Feb 2013 15:57:32 +0900, Alexandre Courbot <acourbot@nvidia.com> wrote:
> On Wed, Feb 6, 2013 at 2:53 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Sat, Feb 2, 2013 at 5:29 PM, Alexandre Courbot <acourbot@nvidia.com> wrote:
> >> +/**
> >> + * Convert a GPIO number to its descriptor
> >> + */
> >> +static struct gpio_desc *gpio_to_desc(unsigned gpio)
> >> +{
> >> + if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))
> >> + return NULL;
> >
> > Don't we want to return ERR_PTR(-EINVAL); here?
> >
> > Then you can use IS_ERR() on the pointers later.
> >
> > This is the approach taken by the external API for clk
> > and pins.
>
> Yes, that completely makes sense.
>
No, it does not. The ERR_PTR()/IS_ERR() is a horrible pattern for code
readability because it breaks the expectations that programmers have for
what is and is not a bad pointer. There are decades of history where the
test for a bad pointer is 'if (!ptr)'. Not only does ERR_PTR make make
that test not work, but the compiler won't tell you when you get it
wrong.
There are places where ERR_PTR makes sense. Particularly when
communicating with userspace where error codes have very specific
meanings, but I don't want it in the GPIO subsystem.
g.
WARNING: multiple messages have this Message-ID (diff)
From: grant.likely@secretlab.ca (Grant Likely)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 6/9] gpiolib: use descriptors internally
Date: Sat, 09 Feb 2013 09:17:29 +0000 [thread overview]
Message-ID: <20130209091729.978C73E1A18@localhost> (raw)
In-Reply-To: <CAAVeFu+phNtzzj7rw96g9iH8sj9gGqd5SfAqtkDHvu3PeL_oQA@mail.gmail.com>
On Thu, 7 Feb 2013 15:57:32 +0900, Alexandre Courbot <acourbot@nvidia.com> wrote:
> On Wed, Feb 6, 2013 at 2:53 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Sat, Feb 2, 2013 at 5:29 PM, Alexandre Courbot <acourbot@nvidia.com> wrote:
> >> +/**
> >> + * Convert a GPIO number to its descriptor
> >> + */
> >> +static struct gpio_desc *gpio_to_desc(unsigned gpio)
> >> +{
> >> + if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))
> >> + return NULL;
> >
> > Don't we want to return ERR_PTR(-EINVAL); here?
> >
> > Then you can use IS_ERR() on the pointers later.
> >
> > This is the approach taken by the external API for clk
> > and pins.
>
> Yes, that completely makes sense.
>
No, it does not. The ERR_PTR()/IS_ERR() is a horrible pattern for code
readability because it breaks the expectations that programmers have for
what is and is not a bad pointer. There are decades of history where the
test for a bad pointer is 'if (!ptr)'. Not only does ERR_PTR make make
that test not work, but the compiler won't tell you when you get it
wrong.
There are places where ERR_PTR makes sense. Particularly when
communicating with userspace where error codes have very specific
meanings, but I don't want it in the GPIO subsystem.
g.
next prev parent reply other threads:[~2013-02-09 9:17 UTC|newest]
Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-02 16:29 [PATCH 0/9] gpiolib: remove gpio_desc[] static array Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-02 16:29 ` [PATCH 1/9] gpiolib: link all gpio_chips using a list Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 17:00 ` Linus Walleij
2013-02-05 17:00 ` Linus Walleij
2013-02-09 9:20 ` Grant Likely
2013-02-09 9:20 ` Grant Likely
2013-02-02 16:29 ` [PATCH 2/9] gpiolib: use gpio_chips list in gpiolib_sysfs_init Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 17:04 ` Linus Walleij
2013-02-05 17:04 ` Linus Walleij
2013-02-09 9:22 ` Grant Likely
2013-02-09 9:22 ` Grant Likely
2013-02-09 9:22 ` Grant Likely
2013-02-02 16:29 ` [PATCH 3/9] gpiolib: use gpio_chips list in gpiochip_find Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 17:05 ` Linus Walleij
2013-02-05 17:05 ` Linus Walleij
2013-02-09 9:25 ` Grant Likely
2013-02-09 9:25 ` Grant Likely
2013-02-09 9:25 ` Grant Likely
2013-02-02 16:29 ` [PATCH 4/9] gpiolib: use gpio_chips list in sysfs ops Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 17:15 ` Linus Walleij
2013-02-05 17:15 ` Linus Walleij
2013-02-09 9:37 ` Grant Likely
2013-02-09 9:37 ` Grant Likely
2013-02-09 9:37 ` Grant Likely
2013-02-09 13:53 ` Alexandre Courbot
2013-02-09 13:53 ` Alexandre Courbot
2013-02-02 16:29 ` [PATCH 5/9] gpiolib: use gpio_chips list in gpiochip_find_base Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 17:21 ` Linus Walleij
2013-02-05 17:21 ` Linus Walleij
2013-02-06 4:48 ` Alex Courbot
2013-02-06 4:48 ` Alex Courbot
2013-02-09 9:47 ` Grant Likely
2013-02-09 9:47 ` Grant Likely
2013-02-02 16:29 ` [PATCH 6/9] gpiolib: use descriptors internally Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 17:53 ` Linus Walleij
2013-02-05 17:53 ` Linus Walleij
2013-02-07 6:57 ` Alexandre Courbot
2013-02-07 6:57 ` Alexandre Courbot
2013-02-09 9:17 ` Grant Likely [this message]
2013-02-09 9:17 ` Grant Likely
2013-02-09 9:17 ` Grant Likely
2013-02-11 14:09 ` Linus Walleij
2013-02-11 14:09 ` Linus Walleij
2013-02-11 15:40 ` Paul Mundt
2013-02-11 15:40 ` Paul Mundt
2013-02-11 17:39 ` Stephen Warren
2013-02-11 17:39 ` Stephen Warren
2013-02-12 12:29 ` Linus Walleij
2013-02-12 12:29 ` Linus Walleij
2013-02-12 15:59 ` Paul Mundt
2013-02-12 15:59 ` Paul Mundt
2013-02-12 17:18 ` Arnd Bergmann
2013-02-12 17:18 ` Arnd Bergmann
2013-02-09 13:11 ` Grant Likely
2013-02-09 13:11 ` Grant Likely
2013-02-09 13:11 ` Grant Likely
2013-02-09 13:11 ` Grant Likely
2013-02-09 14:15 ` Alexandre Courbot
2013-02-09 14:15 ` Alexandre Courbot
2013-02-09 13:24 ` Grant Likely
2013-02-09 13:24 ` Grant Likely
2013-02-09 13:24 ` Grant Likely
2013-02-09 13:24 ` Grant Likely
2013-02-09 14:18 ` Alexandre Courbot
2013-02-09 14:18 ` Alexandre Courbot
2013-02-02 16:29 ` [PATCH 7/9] gpiolib: let gpio_chip reference its descriptors Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 18:00 ` Linus Walleij
2013-02-05 18:00 ` Linus Walleij
2013-02-09 13:28 ` Grant Likely
2013-02-09 13:28 ` Grant Likely
2013-02-02 16:29 ` [PATCH 8/9] gpiolib: use gpio_chips list in gpio_to_desc Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 18:01 ` Linus Walleij
2013-02-05 18:01 ` Linus Walleij
2013-02-05 18:01 ` Linus Walleij
2013-02-09 9:58 ` Grant Likely
2013-02-09 9:58 ` Grant Likely
2013-02-09 9:58 ` Grant Likely
2013-02-09 9:58 ` Grant Likely
2013-02-09 14:21 ` Alexandre Courbot
2013-02-09 14:21 ` Alexandre Courbot
2013-02-09 14:37 ` Grant Likely
2013-02-09 14:37 ` Grant Likely
2013-02-02 16:29 ` [PATCH 9/9] gpiolib: dynamically allocate descriptors array Alexandre Courbot
2013-02-02 16:29 ` Alexandre Courbot
2013-02-05 18:02 ` Linus Walleij
2013-02-05 18:02 ` Linus Walleij
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