linux-kernel - Re: [PATCH 1/2] genirq/msi, platform-msi: Adjust return value of msi_domain_prepare

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Date:   Fri, 2 Jun 2023 09:10:08 +0800
From:   "bibo, mao" <maobibo@...ngson.cn>
To:     Thomas Gleixner <tglx@...utronix.de>,
        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()



在 2023/5/30 23:03, Thomas Gleixner 写道:
> 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.

It is not common issue, command line and documentation explanation
is not suitable here.

Can we add weak function like this?
int __weak arch_set_max_msix_vectors(void)

Regards
Bibo, mao
> 
> Thanks,
> 
>         tglx