linux-kernel - Re: [PATCH v15 00/15] PCI: EP: Add RC-to-EP doorbell with platform MSI controller

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Message-ID: <Z89U4Sa1SqBPLNrm@lizhi-Precision-Tower-5810>
Date: Mon, 10 Mar 2025 17:08:49 -0400
From: Frank Li <Frank.li@....com>
To: Thomas Gleixner <tglx@...utronix.de>, Marc Zyngier <maz@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Anup Patel <apatel@...tanamicro.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Shuah Khan <shuah@...nel.org>, Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Rob Herring <robh@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Niklas Cassel <cassel@...nel.org>, dlemoal@...nel.org,
	jdmason@...zu.us, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
	linux-kselftest@...r.kernel.org, imx@...ts.linux.dev,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v15 00/15] PCI: EP: Add RC-to-EP doorbell with platform
 MSI controller

On Sat, Mar 01, 2025 at 07:09:35PM +0100, Thomas Gleixner wrote:
> On Sat, Mar 01 2025 at 12:02, Marc Zyngier wrote:
> > - This IMMUTABLE thing serves no purpose, because you don't randomly
> >   plug this end-point block on any MSI controller. They come as part
> >   of an SoC.
>
> Yes and no. The problem is that the EP implementation is meant to be a
> generic library and while GIC-ITS guarantees immutability of the
> address/data pair after setup, there are architectures (x86, loongson,
> riscv) where the base MSI controller does not and immutability is only
> achieved when interrupt remapping is enabled. The latter can be disabled
> at boot-time and then the EP implementation becomes a lottery across
> affinity changes.
>
> That was my concern about this library implementation and that's why I
> asked for a mechanism to ensure that the underlying irqdomain provides a
> immutable address/data pair.
>
> So it does not matter for GIC-ITS, but in the larger picture it matters.

Marc:
	Do you satisfy Thomans's anwser? So I can respin this series.

Frank

>
> Thanks,
>
>         tglx