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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Huacai Chen <chenhuacai@loongson.cn>,
        Marc Zyngier <maz@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>
Cc:     linux-kernel@vger.kernel.org, loongson-kernel@lists.loongnix.cn,
        Xuefeng Li <lixuefeng@loongson.cn>,
        Huacai Chen <chenhuacai@gmail.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Huacai Chen <chenhuacai@loongson.cn>
Subject: Re: [PATCH 1/2] genirq/msi, platform-msi: Adjust return value of
 msi_domain_prepare_irqs()
In-Reply-To: <20230527054633.704916-2-chenhuacai@loongson.cn>
References: <20230527054633.704916-1-chenhuacai@loongson.cn>
 <20230527054633.704916-2-chenhuacai@loongson.cn>
Date:   Sat, 27 May 2023 16:03:29 +0200
Message-ID: <87pm6llvm6.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Sat, May 27 2023 at 13:46, Huacai Chen wrote:
> Adjust the return value semanteme of msi_domain_prepare_irqs(), which
> allows us to modify the input nvec by overriding the msi_domain_ops::
> msi_prepare(). This is necessary for the later patch.
>
> Before:
> 0 on success, others on error.
>
> After:
> = 0: Success;
>> 0: The modified nvec;
> < 0: Error code.

This explains what the patch does, but provides zero justification for
this nor any analysis why this is correct for the existing use cases.

That longsoon MSI domain is a PCI MSI domain. PCI/MSI has already a
mechanism to return the actual possible number of vectors if the
underlying space is exhausted.

Why is that not sufficient for your problem at hand?

Thanks,

        tglx