Re: [PATCH v3 3/5] gpio: gpiolib: Allow free() callback to be overridden

On Thu, 12 May 2022 18:55:38 +0100,
"Lad, Prabhakar" [off-list ref] wrote:

Hi Marc,

On Thu, May 12, 2022 at 5:26 PM Marc Zyngier [off-list ref] wrote:

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On Thu, 12 May 2022 14:50:05 +0100,
"Lad, Prabhakar" [off-list ref] wrote:

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Hi Marc,

On Thu, May 12, 2022 at 2:24 PM Marc Zyngier [off-list ref] wrote:

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On Thu, 12 May 2022 13:48:53 +0100,
"Lad, Prabhakar" [off-list ref] wrote:

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Hi Marc,

Thank you for the review.

On Thu, May 12, 2022 at 12:19 PM Marc Zyngier [off-list ref] wrote:

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On Wed, 11 May 2022 19:32:08 +0100,
Lad Prabhakar [off-list ref] wrote:

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Allow free() callback to be overridden from irq_domain_ops for
hierarchical chips.

This allows drivers to free any resources which are allocated during
populate_parent_alloc_arg().

Do you mean more than the fwspec? I don't see this being used.

The free callback is used in patch 5/5 where free is overridden by
rzg2l_gpio_irq_domain_free. I just gave an example there as an
populate_parent_alloc_arg()  In actual in the child_to_parent_hwirq
callback I am using a bitmap [0] to get a free tint slot, this bitmap
needs freeing up when the GPIO interrupt is released from the driver
that as when overridden free callback frees the allocated tint slot so
that its available for re-use.

Right, so that's actually a different life-cycle, and the whole
populate_parent_alloc_arg() is a red herring. What you want is to free
resources that have been allocated via some other paths. It'd be good

Is there any other path which I have missed where I can free up resources?

No, that's the only one. It is just that usually, the alloc()
callback is where you are supposed to perform... allocations.

OK.

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It'd be good if you could move your allocation there, as I would
expect calls to child_to_parent_hwirq() to be idempotent.

For now I'll go with the current implementation, as currently a an
array is maintained which is tied with the tint slot and child (which
is obtained from child_to_parent_hwirq)

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if your commit message actually reflected this instead of using an
example that doesn't actually exist.

My bad, I will update the commit message.

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There is also the question of why we need to have dynamic allocation
for the fwspec itself. Why isn't that a simple stack allocation in the
context of gpiochip_hierarchy_irq_domain_alloc()?

you mean gpio core itself should handle the fwspec
allocation/freeing?

Yes. The only reason we resort to dynamic allocation is because
ThunderX is using MSI-based GPIOs, and thus doesn't use a fwspec (no
firmware is involved here).

I see..

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If we had a union of the two types, we could just have a stack
variable, and pass that along, completely sidestepping the whole
dynamic allocation/freeing business.

Right agreed.

FWIW, I've just posted a PoC patch[1].

I guess I'll have to rebase my changes on top of it now ;)

Not yet. Let's see what people say about it.

	M.

-- 
Without deviation from the norm, progress is not possible.