Re: [PATCH] gpio: extend gpiod_get*() with flags parameter

From: Lee Jones <lee.jones@linaro.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-wireless@vger.kernel.org,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Wolfram Sang <wsa@the-dreams.de>, Takashi Iwai <tiwai@suse.de>,
	linux-mmc@vger.kernel.org,
	Linus Walleij <linus.walleij@linaro.org>,
	Chris Ball <chris@printf.net>,
	dri-devel@lists.freedesktop.org,
	Liam Girdwood <lgirdwood@gmail.com>,
	Peter Ujfalusi <peter.ujfalusi@ti.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Pavel Machek <pavel@ucw.cz>, Jiri Slaby <jslaby@suse.cz>,
	gnurou@gmail.com, Florian Fainelli <f.fainelli@gmail.com>,
	Samuel Ortiz <sameo@linux.intel.com>,
	Alexander Shiyan <shc_work@mail.ru>,
	Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>,
	Jingoo Han <jg1.han@samsung.com>,
	Paul Handrigan <Paul.Handrigan@cirrus.com>,
	linux-iio@vger.kernel.org, linux-omap@vger.kernel.org,
	Tomi Valkeinen <tomi.valkeinen@ti.com>,
	Hans Verkuil <hans.verkuil@ci>
Subject: Re: [PATCH] gpio: extend gpiod_get*() with flags parameter
Date: Fri, 25 Jul 2014 07:52:50 +0100	[thread overview]
Message-ID: <20140725065250.GF7063@lee--X1> (raw)
In-Reply-To: <20140724161052.GA15615@kroah.com>

On Thu, 24 Jul 2014, Greg Kroah-Hartman wrote:

> On Fri, Jul 25, 2014 at 12:04:58AM +0900, Alexandre Courbot wrote:
> > The huge majority of GPIOs have their direction and initial value set
> > right after being obtained by one of the gpiod_get() functions. The
> > integer GPIO API had gpio_request_one() that took a convenience flags
> > parameter allowing to specify an direction and value applied to the
> > returned GPIO. This feature greatly simplifies client code and ensures
> > errors are always handled properly.
> > 
> > A similar feature has been requested for the gpiod API. Since GPIOs need
> > a direction to be used anyway, we prefer to extend the existing
> > functions instead of introducing new functions that would raise the
> > number of gpiod getters to 16 (!).
> > 
> > The drawback of this approach is that all gpiod clients need to be
> > updated, but there aren't that many and the moment and this results in
> > smaller (and hopefully safer) code.
> > 
> > Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> > ---
> > This change will be difficult to apply without breaking things, but
> > let's try to do it right. Hopefully the benefit will outweight the
> > disturbance.
> > 
> > This is a patch against -next to list and update all current gpiod
> > consumers. Updates are trivial at first sight, but it would be nice to
> > get as many acks as possible from the respective subsystem maintainers.
> > 
> > I'm not sure how this could be applied harmlessly though - maybe through
> > a dedicated branch for -next? Problem is that a lot of new code is not
> > yet merged into mainline, and conflicts are very likely to occur. Linus,
> > do you have any suggestion as to how this can be done without blood being
> > spilled?
> 
> Do this in 3 steps, not all at once.
> 
> Make a new function that takes the new argument, get that merged
> 
> Submit patches that convert drivers over to use the new function.
> 
> Once all of those are merged, remove the old function.
> 
> That way there are no "flag days" needed, and everyone is happy you
> don't send out emails with 40+ people in the To: and Cc: lines :)

+99999

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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