2014-11-03 16:43 GMT+03:00 Linus Walleij linus.walleij@linaro.org:
On Fri, Oct 31, 2014 at 10:39 AM, Dmitry Eremin-Solenikov dbaryshkov@gmail.com wrote:
2014-10-31 10:48 GMT+03:00 Linus Walleij linus.walleij@linaro.org:
On Tue, Oct 28, 2014 at 1:01 AM, Dmitry Eremin-Solenikov dbaryshkov@gmail.com wrote:
Add gpiolib driver for gpio pins placed on the LoCoMo GA.
Signed-off-by: Dmitry Eremin-Solenikov dbaryshkov@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?