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

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Date: Tue, 25 Jun 2024 09:55:56 -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 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

Thanks,
Nícolas