linux-kernel - Re: Need clarity on MSI handling in RC driver

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Message-ID: <da4f909c-54ff-530f-93a4-f77642ec9195@gmail.com>
Date:   Fri, 6 Jan 2017 08:00:35 +0530
From:   valmiki <valmikibow@...il.com>
To:     Marc Zyngier <marc.zyngier@....com>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Cc:     helgaas@...nel.org, arnd@...db.de, mark.rutland@....com
Subject: Re: Need clarity on MSI handling in RC driver

Thanks Marc

On 1/4/2017 11:16 PM, Marc Zyngier wrote:
> On 04/01/17 17:39, valmiki wrote:
>> Hi All,
>>
>> I have a doubt, the MSI domains are handled differently in different RC
>> drivers.
>>
>> Some drivers use irq_domain_add_linear alone, and some use
>> pci_msi_create_irq_domain also to handle MSI.
>>
>> In most of the 32-bit architectures only irq_domain_add_linear is used
>> and in 64 bit drivers both pci_msi_create_irq_domain and
>> irq_domain_add_linear are used.
>>
>> So is this because of architecture difference between ARM and ARM64 ?
>
> Neither. This is purely a software construct. Newer drivers use the
> generic MSI infrastructure (which also allows things like non-PCI MSI),
> while older drivers use some ad-hoc infrastructure which is more or less
> specific to PCI.
>
> The former is the way to go, and the latter is being phased out.
>
> I'll let Mark draw some shiny ASCII art.
>
> Thanks,
>
> 	M.
>