Re: [PATCH v6 03/13] gpio: mxc: fix wakeup_pads bit operations

[Peng Fan <peng.fan@oss.nxp.com>]

On Mon, Oct 12, 2026 at 01:30:04PM +0300, Andy Shevchenko wrote:
>On Mon, Oct 12, 2026 at 12:46 PM Peng Fan <peng.fan@oss.nxp.com> wrote:
>> On Mon, Oct 12, 2026 at 12:15:28PM +0300, Andy Shevchenko wrote:
>> >On Sun, Oct 11, 2026 at 2:54 PM Peng Fan (OSS) <peng.fan@oss.nxp.com> wrote:
>> >>
>> >> gpio_set_wake_irq() can be called concurrently for different pins on
>> >> the same port, so use atomic bitops when modifying wakeup_pads.
>> >
>> >The code doesn't modify any reader part of this member. So, the above
>> >paragraph is incorrect, right? Otherwise it needs to be clarified how
>> >assign_bit() does change anything.
>>
>> I will replace with below:
>>
>> gpio_set_wake_irq() can be called concurrently for different pins on
>> the same port. The IRQ core serializes per irq descriptor, but
>> different pins have different descriptors, so concurrent calls for
>> pins on the same port run without mutual exclusion. The plain |= and
>> &= on wakeup_pads are non-atomic read-modify-write operations that
>> can lose updates when two CPUs modify different bits simultaneously.
>> Replace them with assign_bit() to make the modifications atomic.
>
>Right, but the code does change only the writer side. There is no
>reader side that was changed. So this patch does *not* add any
>atomicity. You also need to check if the reader side already uses
>test_bit() or something like that. Otherwise it makes no sense.

The writer-vs-writer race is the concern: two concurrent
gpio_set_wake_irq() calls for different pins on the same port both do
a non-atomic read-modify-write on the same wakeup_pads word. The old
|= and &= compile to separate load/modify/store instructions that can
interleave, losing one CPU's update.

assign_bit() uses an atomic RMW instruction, so concurrent writers to
different bits in the same word are safe.

The reader side (for_each_set_bit in noirq_suspend, wakeup_pads > 0)
runs in noirq context where no concurrent writer can execute, so
reader atomicity is not needed.

Regards,
Peng