[PATCH v2] gpio/omap: fix off-mode bug: clear debounce clock enable mask on free/reset

Santosh Shilimkar santosh.shilimkar at ti.com
Thu Oct 25 09:19:20 EDT 2012

On Thursday 25 October 2012 06:41 PM, Jon Hunter wrote:
> On 10/25/2012 02:00 AM, Santosh Shilimkar wrote:
>> On Thursday 25 October 2012 04:24 AM, Jon Hunter wrote:
>>> On 10/24/2012 12:10 PM, Kevin Hilman wrote:
>>>> From: Kevin Hilman <khilman at ti.com>
>>>> When a GPIO bank is freed or shutdown, ensure that the banks
>>>> dbck_enable_mask is cleared also.  Otherwise, context restore on
>>>> subsequent off-mode transition will restore previous value from the
>>>> shadow copies (bank->context.debounce*) leading to mismatch state
>>>> between driver state and hardware state.
>>>> This was discovered when board code was doing
>>>>     gpio_request_one()
>>>>     gpio_set_debounce()
>>>>     gpio_free()
>>>> which was leaving the GPIO debounce settings in a confused state.  If
>>>> that GPIO bank is subsequently used with off-mode enabled, bogus state
>>>> would be restored, leaving GPIO debounce enabled which then prevented
>>>> the CORE powerdomain from transitioning.
>>>> To fix, ensure that bank->dbck_enable_mask is cleared when the bank
>>>> is freed/shutdown so debounce state doesn't persist.
>> The freed part is fine but I don't understand why it needs to be done
>> on _a_ gpio irq shutdown callback where IRQs related configuration
>> on that one GPIO needs to be cleared. De-bounce clock is surely not IRQ
>> related configuration.
> If we are freeing the IRQs related to gpio and resetting the gpio, then
> I don't see why we should not. We should not leave the debounce clock on
> if these gpios are no longer being used.
Sure which happens in free() anyways.

>>>> Special thanks to Grazvydas Ignotas for pointing out a bug in an
>>>> earlier version that would've disabled debounce on any runtime PM
>>>> transition.
>>>> Reported-by: Paul Walmsley <paul at pwsan.com>
>>>> Cc: Igor Grinberg <grinberg at compulab.co.il>
>>>> Cc: Grazvydas Ignotas <notasas at gmail.com>
>>>> Signed-off-by: Kevin Hilman <khilman at ti.com>
>>>> ---
>>>> v2: only clear mask in free/shutdown, not in runtime PM paths,
>>>>       clarified changelog
>>>> Applies on v3.7-rc2.
>>>>    drivers/gpio/gpio-omap.c | 1 +
>>>>    1 file changed, 1 insertion(+)
>>>> diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
>>>> index 94cbc84..113b167 100644
>>>> --- a/drivers/gpio/gpio-omap.c
>>>> +++ b/drivers/gpio/gpio-omap.c
>>>> @@ -539,6 +539,7 @@ static void _reset_gpio(struct gpio_bank *bank,
>>>> int gpio)
>>>>        _set_gpio_irqenable(bank, gpio, 0);
>>>>        _clear_gpio_irqstatus(bank, gpio);
>>>>        _set_gpio_triggering(bank, GPIO_INDEX(bank, gpio), IRQ_TYPE_NONE);
>>>> +    bank->dbck_enable_mask = 0;
>>>>    }
>>> Does this need to be ...
>>> +    bank->dbck_enable_mask &= ~(GPIO_BIT(bank, gpio));
>>> +    _gpio_dbck_disable(bank);
>> Yes, its a per bank clock. There is an alternate. See below.
>>> There could be more than one gpio using debounce and so we should only
>>> clear the appropriate bit. Also after clearing a bit we could see if we
>>> can disable the debounce clock too.
>> When I mentioned the clearing in gpio_free() path will do trick, I had
>> something like below in mind.
>> diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
>> index dee2856..8574105 100644
>> --- a/drivers/gpio/gpio-omap.c
>> +++ b/drivers/gpio/gpio-omap.c
>> @@ -629,8 +629,10 @@ static void omap_gpio_free(struct gpio_chip *chip,
>> unsigned offset)
>>        * If this is the last gpio to be freed in the bank,
>>        * disable the bank module.
>>        */
>> -    if (!bank->mod_usage)
>> +    if (!bank->mod_usage) {
>> +        bank->dbck_enable_mask = 0;
>>           pm_runtime_put(bank->dev);
>> +    }
> However, with this we could be leaving the debounce clock on longer than
> needed. I think we need to call _gpio_dbck_disable() each time we free a
> gpio and this function will determine if it can turn off the debounce
> clock.
The point is you can't disable the debounce clock if the back in use.
But I get your point. In case other in use GPIOs from bank doesn't
need debouce feature, we can turn off the debouce clock.

> In fact, there appears to be another bug in the current driver, that we
> do not clear the debounce_en register when freeing the gpio. Your patch
> addresses this, but I think that debounce should be disabled when a gpio
> is freed and not just when the last one is freed.
I agree. Just go ahead and spin the patch.

> Also, with the above change, can't we still run into the original
> problem? In other words, if a gpio is freed, but there is still another
> one active in the back that is not using debounce, then we could restore
> a incorrect debounce context because we have not clean-up the debounce
> settings?
Yep. Just mentioned above.

> So may be we need to add a _clear_gpio_debounce() function and
> call this when freeing a gpio.
Sounds good. This function can track the debounce back usage
and based on that do the deb-ounce clean-up.


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