Re: [PATCH 2/5] gpio: Cygnus: add GPIO driver

From: Ray Jui
Date: Fri Dec 05 2014 - 22:42:16 EST

On 12/5/2014 6:34 PM, Joe Perches wrote:
On Fri, 2014-12-05 at 18:14 -0800, Ray Jui wrote:
On 12/5/2014 5:28 PM, Joe Perches wrote:
On Fri, 2014-12-05 at 16:40 -0800, Ray Jui wrote:
+static void bcm_cygnus_gpio_irq_handler(unsigned int irq,
+ struct irq_desc *desc)
+ struct bcm_cygnus_gpio *cygnus_gpio;
+ struct irq_chip *chip = irq_desc_get_chip(desc);
+ int i, bit;
+ chained_irq_enter(chip, desc);
+ cygnus_gpio = irq_get_handler_data(irq);
+ /* go through the entire GPIO banks and handle all interrupts */
+ for (i = 0; i < cygnus_gpio->num_banks; i++) {
+ unsigned long val = readl(cygnus_gpio->base +
+ (i * GPIO_BANK_SIZE) +
+ if (val) {

This if (val) and indentation isn't really necessary

Note for_each_set_bit in this case iterates 32 times searching for bits
that are set.

No it doesn't.

#define for_each_set_bit(bit, addr, size) \
for ((bit) = find_first_bit((addr), (size)); \
(bit) < (size); \
(bit) = find_next_bit((addr), (size), (bit) + 1))


* Returns the bit number of the first set bit.
* If no bits are set, returns @size.

You are right. I reviewed for_each_set_bit but didn't notice find_next_bit may simply return 32 in our case without doing any iterative processing. I will get rid of the redundant if (val) check below.

By having the if (val) check here, it can potentially save
some of such processing in the ISR. I agree with you that it introduces
one extra indent here but I think it's required.

+ for_each_set_bit(bit, &val, 32) {

for_each_set_bit will effectively do the if above.

32 bit only code?
otherwise isn't this endian unsafe?

Will change 'unsigned long val' to 'u32 val'.

All the bit operations only work on long *

Actually, by reviewing the code more deeply, I'm not sure why using for_each_set_bit here is 'endian unsafe'. Isn't that already taken care of by macros in bitops.h? Sorry if I'm still missing something here...
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