Re: [PATCH v2 1/3] gpio: xgene: add support to configure GPIO line as input, output or external IRQ pin

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Oct 26, 2015 at 7:49 AM, Y Vo <yvo@xxxxxxx> wrote:

> Add support to configure GPIO line as input, output or external IRQ pin.
>
> Signed-off-by: Y Vo <yvo@xxxxxxx>

As I will say again, this description is too terse, add lots of information
on how IRQs work on this controller please. I get confused.

(...)

> +#define XGENE_GPIO8_HWIRQ              0x48
> +#define XGENE_GPIO8_IDX                        8
(...)
> +#define XGENE_HWIRQ_TO_GPIO(hwirq)     ((hwirq) + XGENE_GPIO8_IDX)
> +#define XGENE_GPIO_TO_HWIRQ(gpio)      ((gpio) - XGENE_GPIO8_IDX)
> +#define GIC_IRQ_TO_GPIO_IRQ(hwirq)     ((hwirq) - XGENE_GPIO8_HWIRQ)
> +#define GPIO_IRQ_TO_GIC_IRQ(hwirq)     ((hwirq) + XGENE_GPIO8_HWIRQ)

I'm a bit uneasy about this, maybe I just don't get it.

What is this indexing into "GIC IRQ" that is starting to happen
here?

The GIC (if that is drivers/irqchip/irq-gic.c) has a totally dynamic IRQ
translation and the Linux IRQs it is using may change. I am worried
that there is some reliance here on Linux IRQ having certain numbers
because there is certainly no ABI like that.

Is this 0x48 really an index into the *hardware* offset in the GIC?

And if it is: why are we not getting this hardware information from the
device tree like all other interrupt numbers and offsets?

I'm worried about this.

> -       u32 *irq;
> +       void __iomem *regs;
> +       struct irq_domain *gic_domain;
> +       struct irq_domain *irq_domain;

And there is some secondary gic_domain here, which is confusing
since the GIC does have an IRQ domain too.

I think I want a clear explanation to how this GPIO controller interacts
with the GIC, and I want it to be part of the patch, as comments in the
code and in the commit message (which is way too small for a complex
patch like this).

Otherwise I have no chance to understand what is really going on here.

> +static int xgene_gpio_sb_irq_set_type(struct irq_data *d, unsigned int type)
> +{
> +       int hwirq = d->hwirq;
> +       int gpio = XGENE_HWIRQ_TO_GPIO(hwirq);
> +       struct xgene_gpio_sb *priv = irq_data_get_irq_chip_data(d);
> +       int lvl_type;
> +       int ret;
> +
> +       switch (type & IRQ_TYPE_SENSE_MASK) {
> +       case IRQ_TYPE_EDGE_RISING:
> +       case IRQ_TYPE_LEVEL_HIGH:
> +               lvl_type = GPIO_INT_LVL_LEVEL_HIGH;
> +               break;
> +       case IRQ_TYPE_EDGE_FALLING:
> +       case IRQ_TYPE_LEVEL_LOW:
> +               lvl_type = GPIO_INT_LVL_LEVEL_LOW;
> +               break;
> +       default:
> +               return -EINVAL;
> +       }
> +
> +       ret = gpiochip_lock_as_irq(&priv->bgc.gc, gpio);
> +       if (ret) {
> +               dev_err(priv->bgc.gc.dev,
> +               "Unable to configure XGene GPIO standby pin %d as IRQ\n",
> +                                                               gpio);
> +               return ret;
> +       }
> +
> +       if ((gpio >= XGENE_GPIO8_IDX) &&
> +                       (hwirq < XGENE_MAX_GPIO_DS_IRQ)) {
> +               xgene_gpio_set_bit(&priv->bgc, priv->regs + MPA_GPIO_SEL_LO,
> +                               gpio * 2, 1);
> +               xgene_gpio_set_bit(&priv->bgc, priv->regs + MPA_GPIO_INT_LVL,
> +                               hwirq, lvl_type);
> +       }
> +       if (type & (IRQ_TYPE_EDGE_RISING | IRQ_TYPE_EDGE_FALLING))
> +               irq_set_handler_locked(d, handle_edge_irq);
> +       else
> +               irq_set_handler_locked(d, handle_level_irq);
> +
> +       return 0;
> +}

If you are assigning hadle_edge_irq() your irqchip *must* have an
.irq_ack() callback that acknowledges the IRQs as they come in.

This makes me suspect that you haven't really tested edge
interrupts, because if you did, the kernel would crash as it
is unconditionally calling the .irq_ack() from handle_level_irq().

Yours,
Linus Walleij
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