Re: [PATCH] gpio: omap: Silence lockdep "Invalid wait context"

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Tue, Nov 26, 2024 at 9:59 PM Sverdlin, Alexander
<alexander.sverdlin@xxxxxxxxxxx> wrote:
>
> Hi Bartosz!
>
> On Tue, 2024-11-26 at 21:37 +0100, Bartosz Golaszewski wrote:
> > > @@ -647,6 +656,13 @@ static void omap_gpio_irq_shutdown(struct irq_data *d)
> > >          unsigned long flags;
> > >          unsigned offset = d->hwirq;
> > >
> > > +       /*
> > > +        * Enable the clock here so that the nested clk_disable() in the
> > > +        * following omap_clear_gpio_debounce() is lockless
> > > +        */
> > > +       if (bank->dbck_flag)
> > > +               clk_enable(bank->dbck);
> > > +
> >
> > But this looks like a functional change. You effectively bump the
> > clock enable count but don't add a corresponding clk_disable() in the
> > affected path. Is the clock ever actually disabled then?
> >
> > Am I not getting something?
>
> Actually I though I enable and disable them in the very same function, so for the
> first enable above...
>
> >
> > >          raw_spin_lock_irqsave(&bank->lock, flags);
> > >          bank->irq_usage &= ~(BIT(offset));
> > >          omap_set_gpio_triggering(bank, offset, IRQ_TYPE_NONE);
> > > @@ -656,6 +672,9 @@ static void omap_gpio_irq_shutdown(struct irq_data *d)
> > >                  omap_clear_gpio_debounce(bank, offset);
> > >          omap_disable_gpio_module(bank, offset);
> > >          raw_spin_unlock_irqrestore(&bank->lock, flags);
> > > +
> > > +       if (bank->dbck_flag)
> > > +               clk_disable(bank->dbck);
>                     ^^^^^^^^^^^^^^^^^^^^^^^^
>
> this would be the corresponding disable.
>
> > >   }
> > >
> > >   static void omap_gpio_irq_bus_lock(struct irq_data *data)
> > > @@ -827,6 +846,13 @@ static void omap_gpio_free(struct gpio_chip *chip, unsigned offset)
> > >          struct gpio_bank *bank = gpiochip_get_data(chip);
> > >          unsigned long flags;
> > >
> > > +       /*
> > > +        * Enable the clock here so that the nested clk_disable() in the
> > > +        * following omap_clear_gpio_debounce() is lockless
> > > +        */
> > > +       if (bank->dbck_flag)
> > > +               clk_enable(bank->dbck);
>                     ^^^^^^^^^^^^^^^^^^^^^^
> And for this second enable....
>
> > > +
> > >          raw_spin_lock_irqsave(&bank->lock, flags);
> > >          bank->mod_usage &= ~(BIT(offset));
> > >          if (!LINE_USED(bank->irq_usage, offset)) {
> > > @@ -836,6 +862,9 @@ static void omap_gpio_free(struct gpio_chip *chip, unsigned offset)
> > >          omap_disable_gpio_module(bank, offset);
> > >          raw_spin_unlock_irqrestore(&bank->lock, flags);
> > >
> > > +       if (bank->dbck_flag)
> > > +               clk_disable(bank->dbck);
>                     ^^^^^^^^^^^^^^^^^^^^^^^
> ... this would be the corresponding 2nd disable.
>
> > > +
> > >          pm_runtime_put(chip->parent);
> > >   }
> > >
>
> Aren't they paired from your PoV?
>

Ok, I needed to take a long look at this driver.

IIUC what happens now:

In omap_gpio_irq_shutdown() and omap_gpio_free() you now enable the
clock (really just bumping its enable count) before entering
omap_clear_gpio_debounce() so that its internal call do clk_disable()
only decreases the reference count without actually disabling it and
the clock is really disabled one level up the stack.

If that's correct, isn't it unnecessarily convoluted?
omap_clear_gpio_debounce() is only called from these two functions so
why not just move the clk_disable() out of it and into them?

Bartosz