[[RFC PATCH]] gpio: gpio-mxc: make sure gpio is input when request IRQ

[list-09_linux_arm@tqsc.de (Markus Niebel)]

Am 22.07.2014 08:28, wrote Shawn Guo:
> On Wed, Jul 16, 2014 at 03:51:04PM +0200, Markus Niebel wrote:
>> From: Markus Niebel <Markus.Niebel@tq-group.com>
>>
>> When requesting an GPIO irq for imx Soc two things are missing:
>> - there is no check, if the GPIO is already requested
>> - there is no check, if the GPIO is configured as input
>>
>> The first case can lead to reconfiguring the GPIO pin from third
>> party while it is used as IRQ pin, second case will (eventually)
>> prevent IRQ from being seen by SOC becaus the pin is driven by
>> Soc
>>
>> This patch tries to implement (logic taken roughly from gpio-omap)
>> - basic check if gpio already requested
>> - if needed requests the gpio and configures as IN.
>> - if gpio is already requested it is only verified if pin is IN
>> - gpio is locked as irq
>>
>> Tested on a not mainlined i.MX6 based hardware with pin configured
>> by bootloader as OUT HIGH and expecting a low active IRQ.
>>
>> Signed-off-by: Markus Niebel <Markus.Niebel@tq-group.com>
>> ---
>>  drivers/gpio/gpio-mxc.c |   35 +++++++++++++++++++++++++++++++++++
>>  1 file changed, 35 insertions(+)
>>
>> diff --git a/drivers/gpio/gpio-mxc.c b/drivers/gpio/gpio-mxc.c
>> index db83b3c..4316a38 100644
>> --- a/drivers/gpio/gpio-mxc.c
>> +++ b/drivers/gpio/gpio-mxc.c
>> @@ -175,6 +175,31 @@ static int gpio_set_irq_type(struct irq_data *d, u32 type)
>>  	u32 gpio = port->bgc.gc.base + gpio_idx;
>>  	int edge;
>>  	void __iomem *reg = port->base;
>> +	int ret = 0;
>> +
>> +	if (!gpiochip_is_requested(&port->bgc.gc, gpio_idx)) {
>> +		char label[32];
>> +
>> +		snprintf(label, 32, "gpio%u-irq", gpio);
>> +		ret = gpio_request_one(gpio, GPIOF_DIR_IN, label);
> 
> I'm not sure it's correct to call gpio_request_one() from .set_irq_type
> hook.  It looks like a API usage violation to me.  It should really be
> called from client driver.

Thats why it is an RFC. I add Linus Walleij to the cc-list.

Let me describe the problem:

Currently client drivers have simply interrupts and interrupt-parent
in their bindings, but no interrupt-gpios. Therefore in this case a
client does not know about a dedicated gpio which is to be requested
and configured.

> 
>> +	} else {
>> +		val = readl(port->base + GPIO_GDIR);
>> +		if (val & BIT(gpio_idx))
>> +			ret = -EINVAL;
> 
> It says that the GPIO is requested by someone, but we're not really sure
> if it's the correct one, i.e. the one is requesting set_irq_type.
> 

Yes, but the current situation is even worse (in my eyes): an IRQ can be requested and an
independend party can request and configure the gpio as output ...

>> +	}
>> +
>> +	if (ret) {
>> +		dev_err(port->bgc.gc.dev, "unable to set gpio_idx %u as IN\n",
>> +			gpio_idx);
>> +		return ret;
>> +	}
> 
> Having said that, I'm not sure any above changes is really necessary.
> If any, I would say only gpiochip_is_requested() check makes some sense,
> but we should just fail out if the GPIO hasn't been requested.  Nothing
> more can be done in there.

Going that way as a consequence a reworked device tree binding for gpio irq is needed
(just like in the platform data days) when providing a gpio number and the client has
to request gpio and irq - correct me if I'm wrong.

Maybe here is something needed with deeper knowledge in the gpio subsystem.

> 
>> +
>> +	ret = gpio_lock_as_irq(&port->bgc.gc, gpio_idx);
>> +	if (ret) {
>> +		dev_err(port->bgc.gc.dev, "unable to lock gpio_idx %u for IRQ\n",
>> +			gpio_idx);
>> +		return ret;
>> +	}
> 
> This and the following changes do make sense to me.
> 
> Shawn
> 
>>  
>>  	port->both_edges &= ~(1 << gpio_idx);
>>  	switch (type) {
>> @@ -231,6 +256,15 @@ static int gpio_set_irq_type(struct irq_data *d, u32 type)
>>  	return 0;
>>  }
>>  
>> +static void gpio_irq_shutdown(struct irq_data *d)
>> +{
>> +	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(d);
>> +	struct mxc_gpio_port *port = gc->private;
>> +	u32 gpio_idx = d->hwirq;
>> +
>> +	gpio_unlock_as_irq(&port->bgc.gc, gpio_idx);
>> +}
>> +
>>  static void mxc_flip_edge(struct mxc_gpio_port *port, u32 gpio)
>>  {
>>  	void __iomem *reg = port->base;
>> @@ -353,6 +387,7 @@ static void __init mxc_gpio_init_gc(struct mxc_gpio_port *port, int irq_base)
>>  	ct->chip.irq_mask = irq_gc_mask_clr_bit;
>>  	ct->chip.irq_unmask = irq_gc_mask_set_bit;
>>  	ct->chip.irq_set_type = gpio_set_irq_type;
>> +	ct->chip.irq_shutdown = gpio_irq_shutdown;
>>  	ct->chip.irq_set_wake = gpio_set_wake_irq;
>>  	ct->regs.ack = GPIO_ISR;
>>  	ct->regs.mask = GPIO_IMR;
>> -- 
>> 1.7.9.5
>>
> 
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