[PATCH 02/15] GPIO: port LoCoMo gpio support from old driver

Dmitry Eremin-Solenikov dbaryshkov at gmail.com
Wed Nov 5 13:33:24 PST 2014

2014-11-03 16:43 GMT+03:00 Linus Walleij <linus.walleij at linaro.org>:
> On Fri, Oct 31, 2014 at 10:39 AM, Dmitry Eremin-Solenikov
> <dbaryshkov at gmail.com> wrote:
>> 2014-10-31 10:48 GMT+03:00 Linus Walleij <linus.walleij at linaro.org>:
>>> On Tue, Oct 28, 2014 at 1:01 AM, Dmitry Eremin-Solenikov
>>> <dbaryshkov at gmail.com> wrote:
>>>> Add gpiolib driver for gpio pins placed on the LoCoMo GA.
>>>> Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov at gmail.com>
>> [skipped]
>>> (etc, everywhere this pattern occurs).
>>>> +static void locomo_gpio_set(struct gpio_chip *chip,
>>>> +               unsigned offset, int value)
>>>> +{
>>>> +       struct locomo_gpio *lg = container_of(chip, struct locomo_gpio, gpio);
>>>> +       unsigned long flags;
>>>> +
>>>> +       spin_lock_irqsave(&lg->lock, flags);
>>>> +
>>>> +       __locomo_gpio_set(chip, offset, value);
>>>> +
>>>> +       spin_unlock_irqrestore(&lg->lock, flags);
>>> If you actually always have to be getting and releasing a spin lock around
>>> the register writes, contemplate using regmap-mmio because that
>>> is part of what it does.
>>> But is this locking really necessary?
>> I have a custom of doing such locking and never having to think about
>> somebody breaking into RMW cycles.
>> Also isn't regmap an overkill here? Wouldn't regmap also do a lock/unlock
>> around each register read/write/RMW?
> Yes that's the point: if you use regmap mmio you get the RMW-locking
> for free, with the regmap implementation.

Just to be more concrete. Currently locomo_gpio_ack_irq() function uses
one lock and one unlock for doing 3 consecutive RMW I I convert locomo
to regmap, will that be 3 lock/unlock calls or still one? (Or maybe I'm
trying to be over-protective here and adding more lock/unlock cycles
won't matter that much?)

Next question: if I have to export regmap to several subdrivers, is it better
to have one big regmap or to have one-map-per-driver approach?

With best wishes

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