linux-kernel - Re: [PATCH] driver core: Don't log intentional skip of device link creation as error

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Message-ID: <575b02aa-6496-492b-b37d-d0612165eda3@notapiano>
Date: Mon, 29 Jul 2024 17:25:22 -0400
From: Nícolas F. R. A. Prado <nfraprado@...labora.com>
To: Saravana Kannan <saravanak@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>, kernel@...labora.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver core: Don't log intentional skip of device link
 creation as error

On Tue, Jun 25, 2024 at 09:56:07AM -0400, Nícolas F. R. A. Prado wrote:
> On Mon, Jun 24, 2024 at 04:53:30PM -0700, Saravana Kannan wrote:
> > On Mon, Jun 24, 2024 at 8:21 AM Nícolas F. R. A. Prado
> > <nfraprado@...labora.com> wrote:
> > >
> > > Commit ac66c5bbb437 ("driver core: Allow only unprobed consumers for
> > > SYNC_STATE_ONLY device links") introduced an early return in
> > > device_link_add() to prevent useless links from being created. However
> > > the calling function fw_devlink_create_devlink() unconditionally prints
> > > an error if device_link_add() didn't create a link, even in this case
> > > where it is intentionally skipping the link creation.
> > >
> > > Add a check to detect if the link wasn't created intentionally and in
> > > that case don't log an error.
> > 
> > Your point is somewhat valid, and I might Ack this. But this really
> > shouldn't be happening a lot. Can you give more context on how you are
> > hitting this?
> 
> Of course. I'm seeing this on the mt8195-cherry-tomato-r2 platform.
> 
> The following error is printed during boot:
> 
>   mediatek-drm-dp 1c500000.edp-tx: Failed to create device link (0x180) with backlight-lcd0
> 
> It doesn't happen with the upstream defconfig, but with the following config
> change it does:
> 
>   -CONFIG_PWM_MTK_DISP=m
>   +CONFIG_PWM_MTK_DISP=y
> 
> That probably changes the order in which the MTK DP and the backlight drivers
> probe, resulting in the error.
> 
> One peculiarity that comes to mind is that the DP driver calls
> devm_of_dp_aux_populate_bus() to run a callback once the panel has finished
> probing. I'm not sure if this could have something to do with the error.
> 
> Full log at https://lava.collabora.dev/scheduler/job/14573149

Hi Saravana,

With the given context for where this issue is happening, what do you think
about this patch?

Thanks,
Nícolas