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Subject: Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc
To:     "Pankaj Bansal (OSS)" <pankaj.bansal@oss.nxp.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
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From:   Hanjun Guo <guohanjun@huawei.com>
Message-ID: <615c6807-c018-92c9-b66a-8afdda183699@huawei.com>
Date:   Tue, 18 Feb 2020 20:24:56 +0800
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Hi Pankaj,

On 2020/2/18 16:00, Pankaj Bansal (OSS) wrote:
[...]
>>>> Side note: would you mind removing the email headers (as above) in your
>>>> replies please ?
>>
>> Read the question above please.
>>
>> [...]
>>
>>>>> 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.
>>>>> Now, we want to represent this BUS (not individual devices connected to
>> bus)
>>>> in IORT table.
>>>>> The only possible way right now we see is that we describe it as Named
>>>> components having a pool of ID mappings.
>>>>> As and when devices are created and attached to bus, we sift through this
>> pool
>>>> to correctly determine the output ID for the device.
>>>>> 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)
>>> and then we use the Platform MSI framework for all children devices of MC
>> bus.
>>> 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