Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc

Hi Pankaj,

On 2020/2/18 16:00, Pankaj Bansal (OSS) wrote:
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Side note: would you mind removing the email headers (as above) in your
replies please ?

Read the question above please.

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As stated above, in Linux MC is a bus (just like PCI bus, AMBA bus etc)
There can be multiple devices attached to this bus. Moreover, we can

dynamically create/destroy these devices.

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Now, we want to represent this BUS (not individual devices connected to

bus)

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in IORT table.

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The only possible way right now we see is that we describe it as Named

components having a pool of ID mappings.

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As and when devices are created and attached to bus, we sift through this

pool

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to correctly determine the output ID for the device.

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Now the input ID that we provide, can come from device itself.
Then we can use the Platform MSI framework for MC bus devices.

So are you asking me if that's OK ? Or there is something you can't
describe with IORT ?

I am asking if that would be acceptable?
i.e. we represent MC bus as Named component is IORT table with a pool of IDs

(without single ID mapping flag)

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and then we use the Platform MSI framework for all children devices of MC

bus.

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Note that it would require the Platform MSI layer to correctly pass an input id

for a platform device to IORT layer.

How is this solved in DT ? You don't seem to need any DT binding on top
of the msi-parent property, which is equivalent to IORT single mappings
AFAICS so I would like to understand the whole DT flow (so that I
understand how this FSL bus works) before commenting any further.

In DT case, we create the domain DOMAIN_BUS_FSL_MC_MSI for MC bus and it's children.
And then when MC child device is created, we search the "msi-parent" property from the MC
DT node and get the ITS associated with MC bus. Then we search DOMAIN_BUS_FSL_MC_MSI
on that ITS. Once we find the domain, we can call msi_domain_alloc_irqs for that domain.

This is exactly what we tried to do initially with ACPI. But the searching DOMAIN_BUS_FSL_MC_MSI
associated to an ITS, is something that is part of drivers/acpi/arm64/iort.c.
(similar to DOMAIN_BUS_PLATFORM_MSI and DOMAIN_BUS_PCI_MSI)

Can you have a look at mbigen driver (drivers/irqchip/irq-mbigen.c) to see if
it helps you?

mbigen is an irq converter to convert device's wired interrupts into MSI
(connecting to ITS), which will alloc a bunch of MSIs from ITS platform MSI
domain at the setup.

Thanks
Hanjun