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Message-ID: <87zg5lj1yb.ffs@tglx>
Date: Tue, 30 May 2023 17:03:56 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Huacai Chen <chenhuacai@...il.com>
Cc: Marc Zyngier <maz@...nel.org>,
Huacai Chen <chenhuacai@...ngson.cn>,
Bjorn Helgaas <bhelgaas@...gle.com>,
linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn,
Xuefeng Li <lixuefeng@...ngson.cn>,
Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH 1/2] genirq/msi, platform-msi: Adjust return value of
msi_domain_prepare_irqs()
On Tue, May 30 2023 at 16:34, Huacai Chen wrote:
> On Tue, May 30, 2023 at 4:19 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>> Let's take a step back and look at the larger picture:
>>
>> 1) A PCI/MSI irqdomain is attached to a PCI bus
>>
>> 2) The number of PCI devices on that PCI bus is usually known at boot
>> time _before_ the first device driver is probed.
>>
>> That's not entirely true for PCI hotplug devices, but that's hardly
>> relevant for an architecture which got designed less than 10 years
>> ago and the architects decided that 256 MSI vectors are good enough
>> for up to 256 CPUs. The concept of per CPU queues was already known
>> at that time, no?
> Does this solution depend on the per-device msi domain? Can we do that
> if we use the global msi domain?
In principle it should not depend on per-device MSI domains, but I
really don't want to add new functionality to the old operating models
as that does not create an incentive for people to convert their stuff
over.
>> So the irqdomain can tell the PCI/MSI core the maximum number of vectors
>> available for a particular bus, right?
>>
>> The default, i.e if the irqdomain does not expose that information,
>> would be "unlimited", i.e. ULONG_MAX.
> OK, thanks, but how to expose? By msi_domain_info::hwsize?
Probably. Needs a proper helper around it.
Thanks,
tglx
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