linux-kernel - Re: Removal of bus->msi assignment breaks MSI with stacked domains

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Message-ID: <20141120215353.GA7987@google.com>
Date:	Thu, 20 Nov 2014 14:53:53 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Yijing Wang <wangyijing@...wei.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-pci@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: Removal of bus->msi assignment breaks MSI with stacked domains

On Thu, Nov 20, 2014 at 04:31:45PM +0000, Marc Zyngier wrote:
> Bjorn, Yijing,
> 
> I've just realized that patch c167caf8d174 (PCI/MSI: Remove useless
> bus->msi assignment) completely breaks MSI on arm64 when using the new
> MSI stacked domain:
> 
> This patch relies on architectures to implement either
> pcibios_msi_controller() or arch_setup_msi_irq(). It turns out that with
> stacked domains, none of this is actually necessary, as long as you can
> access to the msi_controller.
> 
> And everything was fine until this patch came around (and managed to
> test on a system where the PCI devices are not directly attached to the
> root bus). Of course, everything now breaks, as we cannot get to the MSI
> controller (which contains the domain we allocate the MSIs from).
> 
> In short, this patch breaks an important feature on which arm64 relies,
> and I believe this patch should be reverted ASAP.

I'm happy to revert it from pci/msi, but I think Thomas has already pulled
it into his branch, so he'd have to drop it, too.

Thomas, let me know if you want to do that.  I suppose we could add a new
patch to add it back, but that would leave bisection broken for the
interval between c167caf8d174 and the patch that adds it back.

Bjorn
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