linux-kernel - Re: [RFC PATCH v2 09/12] gpiolib: Identify GPIO descriptor arrays with direct mapping

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Date:   Tue, 07 Aug 2018 19:19:57 +0200
From:   Janusz Krzysztofik <jmkrzyszt@...il.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Janusz Krzysztofik <jmkrzyszt@...il.com>
Subject: Re: [RFC PATCH v2 09/12] gpiolib: Identify GPIO descriptor arrays with direct mapping

On Tuesday, August 7, 2018 7:14:20 PM CEST Boris Brezillon wrote:
> On Tue,  7 Aug 2018 00:29:15 +0200
> Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:
> 
> > Certain GPIO array lookup results may map directly to GPIO pins of a
> > single GPIO chip in hardware order.  If that condition is recognized
> > and handled efficiently, significant performance gain of get/set array
> > functions may be possible.
> > 
> > While processing a request for an array of GPIO descriptors, verify if
> > the descriptors just collected represent consecutive pins of a single
> > GPIO chip.  Pass that information with the array to the caller so it
> > can benefit from enhanced performance as soon as bitmap based get/set
> > array functions which can make efficient use of that are available.
> > 
> > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>
> > ---
> >  Documentation/driver-api/gpio/consumer.rst |  4 +++-
> >  drivers/gpio/gpiolib.c                     | 14 ++++++++++++++
> >  include/linux/gpio/consumer.h              |  1 +
> >  3 files changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst
> > index aa03f389d41d..38a990b5f3b6 100644
> > --- a/Documentation/driver-api/gpio/consumer.rst
> > +++ b/Documentation/driver-api/gpio/consumer.rst
> > @@ -109,11 +109,13 @@ For a function using multiple GPIOs all of those can be obtained with one call::
> >  					   enum gpiod_flags flags)
> >  
> >  This function returns a struct gpio_descs which contains an array of
> > -descriptors::
> > +descriptors.  It may also contain a valid descriptor of a single GPIO chip in
> > +case the array strictly matches pin hardware layout of the chip::
> >  
> >  	struct gpio_descs {
> >  		unsigned int ndescs;
> >  		struct gpio_desc *desc[];
> > +		struct gpio_chip *chip;
> 
> chip is placed at the beginning of the struct in the real code, which
> is expected since putting it at the end won't work because of the
> desc[] declaration.

Yes, I've already noticed that and will fix on next iteration, thanks.

Janusz