Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: v4.17 regression: PowerMac G3 won't boot, was Re: [PATCH v5 1/3]
 of: cache phandle nodes to reduce cost of of_find_node_by_phandle()
To:     Finn Thain <fthain@telegraphics.com.au>
Cc:     Stan Johnson <userm57@yahoo.com>, Rob Herring <robh+dt@kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Chintan Pandya <cpandya@codeaurora.org>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
References: <1520208889-3908-1-git-send-email-frowand.list@gmail.com>
 <1520208889-3908-2-git-send-email-frowand.list@gmail.com>
 <alpine.LNX.2.21.1808301025480.73@nippy.intranet>
From:   Frank Rowand <frowand.list@gmail.com>
Message-ID: <0ad5dbfd-08f3-b97d-34b9-70fc9a729921@gmail.com>
Date:   Thu, 30 Aug 2018 21:36:00 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <alpine.LNX.2.21.1808301025480.73@nippy.intranet>
Content-Type: text/plain; charset=windows-1252
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Finn,

On 08/29/18 17:44, Finn Thain wrote:
> Hi Frank,
> 
> Linux v4.17 and later will no longer boot on a G3 PowerMac. The boot hangs 
> very early, before any video driver loads.
> 
> Stan and I were able to bisect the regression between v4.16 and v4.17 and 
> arrived at commit 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of 
> of_find_node_by_phandle()").
> 
> I don't see any obvious bug in 0b3ce78e90fc or b9952b5218ad. But if you 
> revert these from v4.18 (which is also affected) that certainly resolves 
> the issue.
> 
> I did see this in the kernel messages:
> 
> Duplicate name in PowerPC,750, renamed to "l2-cache#1"
> Duplicate name in mac-io, renamed to "ide#1"
> Duplicate name in ide#1, renamed to "atapi-disk#1"
> Duplicate name in multifunc-device, renamed to "pci1799,1#1"
> 
> No idea whether that's relevant; I haven't done any further investigation. 
> Complete dmesg output is attached. Please let me know if there's any more 
> information you need to help find the bug.
> 
> Thanks.

I don't have any useful answers yet, but I am following the thread and have
also quickly scanned the two commits for any obvious cause.  I will look
into this some more, but have a few other tasks that I need to complete
first.

A long shot, but something to consider, is that I failed to cover the
cases of dynamic devicetree updates (removing nodes that contain a
phandle) in ways other than overlays.  Michael Ellerman has reported
such a problem for powerpc/mobility with of_detach_node().  A patch to
fix that is one of the tasks I need to complete.

-Frank