2014-11-03 16:43 GMT+03:00 Linus Walleij [off-list ref]:

On Fri, Oct 31, 2014 at 10:39 AM, Dmitry Eremin-Solenikov
[off-list ref] wrote:

quoted

2014-10-31 10:48 GMT+03:00 Linus Walleij [off-list ref]:

quoted

On Tue, Oct 28, 2014 at 1:01 AM, Dmitry Eremin-Solenikov
[off-list ref] wrote:

quoted

Add gpiolib driver for gpio pins placed on the LoCoMo GA.

Signed-off-by: Dmitry Eremin-Solenikov <redacted>

[skipped]

quoted

(etc, everywhere this pattern occurs).

quoted

+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
Dmitry