linux-kernel - Re: [PATCH] of: property: fw_devlink: Fix stupid bug in remote-endpoint parsing

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Message-ID: <Zf7I65PiOR2wX1Uo@titan>
Date: Sat, 23 Mar 2024 23:19:55 +1100
From: John Watts <contact@...kia.org>
To: Saravana Kannan <saravanak@...gle.com>
Cc: Rob Herring <robh+dt@...nel.org>, Frank Rowand <frowand.list@...il.com>,
	Hervé Codina <herve.codina@...tlin.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>, kernel-team@...roid.com,
	Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: property: fw_devlink: Fix stupid bug in
 remote-endpoint parsing

Hello again,

On Fri, Mar 22, 2024 at 06:53:57PM -0700, Saravana Kannan wrote:
> Hmmm.... cycle detection should work here and not enforce probe
> ordering. I'd appreciate help with debugging that. Let me look at it
> on Monday. Can you enabled all the debug logs in drivers/base/core.c
> and tell me what cycle detection is telling about these nodes?

Hmm. It's not saying anything more than what I've already sent.

I think this is because /sound/multi isn't a device, it's just a
subnode used in audio-graph-card2.
Removing the multi { } section and using direct graph connections
'fixes' this.

I think this might be because usually in a graph each node containing
ports is a device, such as a display panel, a bridge, an LCD
controller. These kind of form a dependency chain.

In this case all the ports in multi act as a way to glue multiple
ports together for the audio-graph-card2.

Does that help?

> But the better fix would be to use the new "post-init-providers"
> property. See below.
> 
> >
> > / {
> >         ...
> >
> >
> >         test_codec {
> >                 compatible = "test-codec";
> >                 prefix = "Test codec";
> >                 #sound-dai-cells = <0>;
> 
> post-init-provider = <&multi>;
> 
> Right now there's a cyclic dependency between test_codec and multi and
> this tells the kernel that test codec needs to probe first.
> 
> Similar additions to the other nodes blocked on multi.
> 
> Thanks,
> Saravana

John.