linux-kernel - Re: [PATCH v2 5/5] irqchip/gic-v3-its: Use allocation size from the prepare call

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Message-ID: <87zff8hk1x.ffs@tglx>
Date: Mon, 19 May 2025 14:16:58 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Sascha Bischoff
 <sascha.bischoff@....com>, Timothy Hayes <timothy.hayes@....com>
Subject: Re: [PATCH v2 5/5] irqchip/gic-v3-its: Use allocation size from the
 prepare call

On Mon, May 19 2025 at 11:15, Marc Zyngier wrote:
> On Sun, 18 May 2025 19:53:42 +0100,
> Thomas Gleixner <tglx@...utronix.de> wrote:
>> 
>> On Tue, May 13 2025 at 17:31, Marc Zyngier wrote:
>> 
>> > Now that .msi_prepare() gets called at the right time and not
>> > with semi-random parameters, remove the ugly hack that tried
>> > to fix up the number of allocated vectors.
>> >
>> > It is now correct by construction.
>> 
>> FWIW, while looking at something related, it occured to me that with
>> this change you can enable MSI_FLAG_PCI_MSIX_ALLOC_DYN now on GIC ITS.
>
> Maybe. It is rather unclear to me what this "dynamic allocation"
> actually provides in terms of guarantees to the endpoint driver.

It allows the driver to avoid allocating a gazillion of interrupts
upfront during initialization. Instead it can allocate them on demand,
when e.g. a queue is initialized. Of course that means that such an
allocation can fail, but so can request_irq() and other things. I'm not
sure what you mean with guarantees here.

Thanks

        tglx