linux-kernel - Re: [PATCH v9 1/6] platform-msi: Add msi_remove_device_irq_domain() in platform_device_msi_free_irqs

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Message-ID: <87plm8s6jy.ffs@tglx>
Date: Wed, 04 Dec 2024 00:14:25 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Frank Li <Frank.li@....com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, Krzysztof
 Wilczyński <kw@...ux.com>, Kishon Vijay Abraham I
 <kishon@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Anup Patel <apatel@...tanamicro.com>,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 imx@...ts.linux.dev, Niklas Cassel <cassel@...nel.org>,
 dlemoal@...nel.org, maz@...nel.org, jdmason@...zu.us, stable@...nel.org
Subject: Re: [PATCH v9 1/6] platform-msi: Add msi_remove_device_irq_domain()
 in platform_device_msi_free_irqs_all()

On Tue, Dec 03 2024 at 16:40, Frank Li wrote:
> On Tue, Dec 03, 2024 at 10:12:36PM +0100, Thomas Gleixner wrote:
>> Sure, but that's not a fix and not required for stable because no
>> existing driver is affected by this unless I'm missing something.
>>
>> What's the actual use case for this? You describe in great length what
>> fails, which is nice, but I'm missing the larger picture here.
>
> PCI host send a door bell to PCI endpoint, which use platform msi to
> trigger a IRQ.
>
> PCI Host side				PCI endpoint side
>
> Send "enable"  command      ->         call platform_device_msi_init_and_alloc_irqs()
> Get doorbell address        <-         send back MSI address by shared memory
> Write data to doorbell      -> 	       MSI irq handler triggered.
> Send "Disable"  command     ->	       call platform_device_msi_free_irqs_all()
>
>
> At endpoint side, need dymatic response "enable/disable" commands. Of
> course, I can call msi_remove_device_irq_domain() in my disable function.
> But I think it should be symetic in alloc/free pair functions.

No objections, but that's not a justification for a stable backport as
nothing in tree has this problem right now. You add a new use case which
requires it, so only that new use case has this dependency, no?

Thanks,

        tglx