Re: [PATCH 4/7] gpio: dwapb: Convert driver to using the GPIO-lib-based IRQ-chip

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Wed, Jul 29, 2020 at 3:58 PM Serge Semin
<Sergey.Semin@baikalelectronics.ru> wrote:
> On Mon, Jul 27, 2020 at 12:22:28AM +0200, Linus Walleij wrote:

...

> Sorry for a delay with a response to this issue. I had to give it a more thorough
> thought since the problem is a bit more complex than it seemed originally. As I
> see it now It might be wrong to implement the cases 2) and 3), but 1) is more
> appropriate.
>
> First of all we need to note that GPIOlib framework provides the next parameters
> to describe the IRQ-chip:
> gc->irq.num_parents - number of parental IRQ numbers.
> gc->irq.parents[] - array of parental IRQ numbers.
> *gc->irq.valid_mask - a mask of IRQ/GPIO lines describing a valid IRQ.
> *gc->irq.map - mapping of hw IRQ/GPIO ID -> parental IRQ numbers.
>
> Using that set we can handle any case of linear and sparse parental IRQs. Here
> is how it can be implemented in the framework of DW APB GPIO controller.
>
> DW APB GPIO can be synthesized with two configs:
> 1) Combined IRQ line (GPIO_INTR_IO == True),
> 2) Multiple interrupt signals for each GPIO (GPIO_INTR_IO == False).
>
> Obviously the former case is trivial:
>
>      IRQ_combined
>     ______^________
>    /_ _ _ _ _ ___ _\
>    |_|_|_|_|_|...|_| - GPIOs
>
> In that case
> gc->irq.num_parents = 1;
> gc->irq.parents[0] = IRQ_combined;
> *gc->irq.valid_mask = GENMASK(ngpio - 1, 0); // This is done by the GPIOlib core itself.
>
> The later one (when multiple interrupt signals are involved) can be a bit more
> complicated. It can be also split up into two cases:
> 2a) One-on-one GPIO-IRQ mapping.
> 2b) Sparse GPIO-IRQ mapping.
>
> It's straightforward to implement 2a):
>
>    i1i2i3i4i5 ... iN
>     _ _ _ _ _ ___ _
>    |_|_|_|_|_|...|_| - GPIOs
>
> In that case
> gc->irq.num_parents = ngpio;
> gc->irq.parents[] = {i1, i2, i3, i4, i5, ... iN};
> gc->irq.map = {i1, i2, i3, i4, i5, ... iN};
> *gc->irq.valid_mask = GENMASK(ngpio - 1, 0);
>

This case puzzles me. Why is it not NULL and 0 and actually you handle
everything as a nested case?

> The complication starts when we get to implementing 2b):
>
>    i1 xi3i4 x ... iN
>     _ _ _ _ _ ___ _
>    |_|_|_|_|_|...|_| - GPIOs

So does this.

Valid mask will define exactly GPIOs that are IRQs. So, we will handle
only nested IRQs which are valid.

> In order to cover this case we need to answer on two question.
> Firstly how to get such platform config? I am not sure about ACPI, but
> aside from straightforward platform_data-based setup such configuration
> can be reached by setting up the "interrupts-extended" DT-property with
> zeroed phandle.
>
> Ok, since it's possible to meet such platform config, we need to think
> how to handle it and here is the second question. How to describe such
> case in the framework of GPIOlib-IRQchip?
>
> So from my side it was wrong to set the sparse IRQs array to
> gc->irq.parents. Instead I should have scanned the sparse IRQs array,
> calculated the number of non-empty parental IRQs, created an array of linear
> (non-sparse) IRQs, initialized *gc->irq.valid_mask in accordance with the
> sparse parental IRQs array. In other words it was wrong to assume, that
> each gc->irq.parents entry corresponds to the IRQ/GPIO line. The gc->irq.parents
> array just describes the parental IRQs and nothing else.
>
> Shortly speaking here is how the GPIOlib IRQchip parameters should be
> initialized in this case:
> gc->irq.num_parents - number of valid parental IRQs.
> gc->irq.parents - non-sparse, linear array of valid IRQs.
> *gc->irq.valid_mask - mask initialized by means of the gc->irq.init_valid_mask()
> callback, which indicates valid IRQ/GPIO IDs.
> *gc->irq.map - sparse array of parental IRQ numbers (which I mistakenly tried to
> pass through the gc->irq.parents pointer).
>
> After that GPIOlib IRQchip should work just fine without need to be patched
> in order to check whether the passed parental IRQs are valid or not.
>
> Please correct me if I am wrong in some aspects of the solution described above.
> I'll send a fix of the problem shortly.

Maybe I'm missing something, but looks like you are solving the issue
which is not so complex / doesn't exist.

-- 
With Best Regards,
Andy Shevchenko