On Mon, Feb 19, 2024 at 4:54 PM Théo Lebrun [off-list ref] wrote:

Hello,

On Mon Feb 19, 2024 at 4:48 PM CET, Bartosz Golaszewski wrote:

quoted

On Wed, Feb 14, 2024 at 5:24 PM Théo Lebrun [off-list ref] wrote:

quoted

Support a single IRQs used by multiple GPIO banks. Change the IRQ
handler type from a chained handler (as used by gpiolib
for ->parent_handler) to a threaded IRQ.

Use a fake raw spinlock to ensure generic_handle_irq() is called in a
no-irq context. See Documentation/driver-api/gpio/driver.rst, "CHAINED
CASCADED GPIO IRQCHIPS" for additional information.

Any reason for not using preempt_disable()?

I did what the doc recommended:

quoted

The generic_handle_irq() is expected to be called with IRQ disabled,
so the IRQ core will complain if it is called from an IRQ handler which is
forced to a thread. The "fake?" raw lock can be used to work around this
problem::

  raw_spinlock_t wa_lock;
  static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank)
      unsigned long wa_lock_flags;
      raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags);
      generic_handle_irq(irq_find_mapping(bank->chip.irq.domain, bit));
      raw_spin_unlock_irqrestore(&bank->wa_lock, wa_lock_flags);

If you confirm I should be using preempt_disable() that's what I'll do
in the next revision. I could even throw in a documentation patch if
the advice is outdated.

Thanks Bartosz,

This was added 9 years ago:

commit c307b002548590c5d8c32b964831de671ad4affe
Author: Grygorii Strashko [off-list ref]
Date:   Tue Oct 20 17:22:15 2015 +0300

    gpio: add a real time compliance notes

    Put in a compliance checklist.

    Signed-off-by: Grygorii Strashko [off-list ref]
    Signed-off-by: Linus Walleij [off-list ref]

I'm Cc'ing Grygorii - maybe he can remember if there was any reason
for using a spinlock over preempt_disable(). But for now I'd go with
the latter.

Bart

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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