Re: [PATCH net-next v8 6/9] net: txgbe: Support GPIO to SFP socket

[Michael Walle <michael@xxxxxxxx>]

Hi, 

I'm currently (and for the next three weeks) on vacation. Sorry in advanced if the format of the mail is wrong or similar. I just have access to my mobile. 

Am 18. Mai 2023 14:27:00 MESZ schrieb Andy Shevchenko <andy.shevchenko@xxxxxxxxx>:
>On Thu, May 18, 2023 at 2:50 PM Jiawen Wu <jiawenwu@xxxxxxxxxxxxxx> wrote:
>> On Wednesday, May 17, 2023 11:01 PM, Andrew Lunn wrote:
>> > On Wed, May 17, 2023 at 10:55:01AM +0800, Jiawen Wu wrote:
>
>...
>
>> > > I should provide gpio_regmap_config.irq_domain if I want to add the gpio_irq_chip.
>> > > But in this use, GPIO IRQs are requested by SFP driver. How can I get irq_domain
>> > > before SFP probe? And where do I add IRQ parent handler?
>> >
>> > I _think_ you are mixing upstream IRQs and downstream IRQs.
>> >
>> > Interrupts are arranged in trees. The CPU itself only has one or two
>> > interrupts. e.g. for ARM you have FIQ and IRQ. When the CPU gets an
>> > interrupt, you look in the interrupt controller to see what external
>> > or internal interrupt triggered the CPU interrupt. And that interrupt
>> > controller might indicate the interrupt came from another interrupt
>> > controller. Hence the tree structure. And each node in the tree is
>> > considered an interrupt domain.
>> >
>> > A GPIO controller can also be an interrupt controller. It has an
>> > upstream interrupt, going to the controller above it. And it has
>> > downstream interrupts, the GPIO lines coming into it which can cause
>> > an interrupt. And the GPIO interrupt controller is a domain.
>> >
>> > So what exactly does gpio_regmap_config.irq_domain mean? Is it the
>> > domain of the upstream interrupt controller? Is it an empty domain
>> > structure to be used by the GPIO interrupt controller? It is very
>> > unlikely to have anything to do with the SFP devices below it.
>>
>> Sorry, since I don't know much about interrupt,  it is difficult to understand
>> regmap-irq in a short time. There are many questions about regmap-irq.
>
>That's why I Cc'ed to Michael who is the author of gpio-regmap to
>probably get advice from.

All gpio remap is doing is forwarding the IRQ domain from regmap-irq to the gpio subsystem. It's opaque to gpio-regmap and outside the scope of gpio-regmap. 

-michael

>> When I want to add an IRQ chip for regmap, for the further irq_domain,
>> I need to pass a parameter of IRQ, and this IRQ will be requested with handler:
>> regmap_irq_thread(). Which IRQ does it mean? In the previous code of using
>> devm_gpiochip_add_data(), I set the MSI-X interrupt as gpio-irq's parent, but
>> it was used to set chained handler only. Should the parent be this IRQ? I found
>> the error with irq_free_descs and irq_domain_remove when I remove txgbe.ko.
>>
>> As you said, the interrupt of each tree node has its domain. Can I understand
>> that there are two layer in the interrupt tree for MSI-X and GPIOs, and requesting
>> them separately is not conflicting? Although I thought so, but after I implement
>> gpio-regmap, SFP driver even could not find gpio_desc. Maybe I missed something
>> on registering gpio-regmap...
>>
>> Anyway it is a bit complicated, could I use this version of GPIO implementation if
>> it's really tough?
>
>It's possible but from GPIO subsystem point of view it's discouraged
>as long as there is no technical impediment to go the regmap way.