Re: [PATCH v4 0/2] Add capability to dump fdt blob for arm64 platforms

From: AKASHI Takahiro <takahiro.akashi@linaro.org>
To: Simon Horman <horms@verge.net.au>
Cc: dyoung@redhat.com, Bhupesh Sharma <bhsharma@redhat.com>,
	bhupesh.linux@gmail.com, kexec@lists.infradead.org,
	james.morse@arm.com
Subject: Re: [PATCH v4 0/2] Add capability to dump fdt blob for arm64 platforms
Date: Wed, 25 Jul 2018 09:32:29 +0900	[thread overview]
Message-ID: <20180725003228.GB11258@linaro.org> (raw)
In-Reply-To: <20180724063110.lclgpne27o5xbws3@verge.net.au>

On Tue, Jul 24, 2018 at 08:31:54AM +0200, Simon Horman wrote:
> On Tue, Jul 17, 2018 at 02:13:42AM +0530, Bhupesh Sharma wrote:
> > Hi Akashi,
> > 
> > On 07/09/2018 12:41 PM, AKASHI Takahiro wrote:
> > > Bhupesh, Simon,
> > > 
> > > #I'm afraid that I gonna rehash the old discussion.
> > > 
> > > Looking into ppc's kexec-tools code, I found that ppc version of
> > > this tool has a similar feature and it saves a new dtb into a file,
> > > named "debug.dtb."
> > > See save_fixed_up_dtb() in kexec/arch/ppc/fixup_dtb.c
> > > 
> > > Even if it is a debug feature, we'd better go in the same way
> > > (if possible).
> > 
> > Thanks for sharing the same.
> > 
> > I had a look earlier also at the ppc - "debug.dtb" code in kexec-tools, but
> > this is again fails to fulfill the same purpose that we are trying to
> > resolve for early primary kernel crash(es) on arm64 machines, because of
> > which we are not able to reach the command prompt with the primary kernel
> > itself.
> > 
> > We would need to either reach the command prompt to dump out/save the
> > "debug.dtb" file when we are running the primary kernel (which is
> > unfortunately not always possible wit latest kernels on some of the arm64
> > machines),

Although I'm not sure how it cannot be possible,

> or use some initramfs scriptware to dump out the same to some
> > secondary storage device (nfs server or usb stick).
> > 
> > So, I would still suggest to stick with the approach I proposed for now (and
> > we can take a similar approach as ppc for arm64 later on) once we have
> > kexec, kdump and other user-space utilities (which rely on the kexec kernel
> > framework) working stably on arm64 machines (with latest upstream kernels).
> 
> That sounds like a reasonable argument to me.
> 
> Akashi, what do you think?

it's fine to me, too.

-Takahiro AKASHI

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