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Date:   Tue, 9 Oct 2018 17:03:27 +0100
From:   Will Deacon <will.deacon@arm.com>
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Keith Busch <keith.busch@intel.com>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Sinan Kaya <okaya@kernel.org>,
        Thomas Tai <thomas.tai@oracle.com>, poza@codeaurora.org,
        Lukas Wunner <lukas@wunner.de>, Christoph Hellwig <hch@lst.de>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/12] error handling and pciehp maintenance
Message-ID: <20181009160327.GE9259@arm.com>
References: <20180918235848.26694-1-keith.busch@intel.com>
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Hi Bjorn,

On Fri, Oct 05, 2018 at 12:31:45PM -0500, Bjorn Helgaas wrote:
> [+cc arm64 folks, LKML: This conversation is about this patch:
> 
>   https://lore.kernel.org/linux-pci/20180918235848.26694-3-keith.busch@intel.com
> 
> which fixes some PCIe AER error injection bugs, but also makes the error
> injector dependent on DYNAMIC_FTRACE_WITH_REGS, which not all arches
> support.  Note that this question is only about the error *injection*
> module used for testing.  It doesn't affect AER support itself.]
> 
> On Thu, Oct 04, 2018 at 04:11:37PM -0600, Keith Busch wrote:
> > In case this went unnoticed, patch 2's aer_inject using ftrace hooks
> > to pci config accessors is really cool and fixes several kernel crashes
> > I encountered, but it may not work on every architecture. I'm not sure
> > how widely aer_inject is used, so maybe there are no concerns with the
> > DYNAMIC_FTRACE_WITH_REGS dependency, but I just want to reemphasize that
> > dependency in case there are valid objections.
> 
> Oh, indeed, I hadn't noticed this arch dependency.  AFAICT, the new
> DYNAMIC_FTRACE_WITH_REGS dependency means aer_inject will work only
> on these arches:
> 
>   arm		# if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU
>   powerpc	# if PPC64 && CPU_LITTLE_ENDIAN
>   riscv		# ARCH_RV64I only
>   s390
>   x86
> 
> Notably missing is arm64, which has DYNAMIC_FTRACE but not
> DYNAMIC_FTRACE_WITH_REGS.

Thanks for the heads-up here. This feature is currently in development for
arm64:

http://lkml.kernel.org/r/20181001141648.1DBED68BDF@newverein.lst.de

but the latest review comments suggest that it's a fair way from ready yet,
so I wouldn't hold your breath.

Will