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

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Message-ID: <3b8ed7fbe4fd879b34b40c74485e2871849ddc93.camel@ew.tq-group.com>
Date: Tue, 17 Dec 2024 14:44:12 +0100
From: Matthias Schiffer <matthias.schiffer@...tq-group.com>
To: Nícolas "F. R. A. Prado" <nfraprado@...labora.com>, 
 Saravana Kannan <saravanak@...gle.com>
Cc: kernel@...labora.com, linux-kernel@...r.kernel.org, Greg Kroah-Hartman
	 <gregkh@...uxfoundation.org>, "Rafael J.Wysocki" <rafael@...nel.org>, 
	linux@...tq-group.com
Subject: Re: [PATCH] driver core: Don't log intentional skip of device link
 creation as error

On Mon, 2024-06-24 at 11:20 -0400, Nícolas F. R. A. Prado 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.


While it was concluded that this patch was not needed to fix the author's issue,
I have come across a similar problem that I have not been able to solve:

I'm currently working on a TI AM335x, and after updating to a recent kernel
(currently 6.12.4) and fixing the ti-sysc driver to probe in a few cases where
it was broken before, I'm now seeing the following messages:

ti-sysc 44e31000.target-module: Failed to create device link (0x180) with ocp
ti-sysc 48040000.target-module: Failed to create device link (0x180) with ocp

The direct cause of the failure is the same as noted in this patch: The
44e31000.target-module and 48040000.target-module devices have already been
probed at this point, so applying it would hide the error message.

The attempt to create these device links results from a call to
__fw_devlink_pickup_dangling_consumers() moving consumers from
/ocp/interrupt-controller@...00000 to /ocp. This happens because the interrupt
controller driver (irq-omap-intc) is declared using IRQCHIP_DECLARE(), so its
fwnode doesn't have an associated device.

As the existence of fwnodes without device is the whole point of
__fw_devlink_pickup_dangling_consumers(), I imagine that this is a valid case
that should be supported properly. Would it make sense to reconsider this patch,
or is there a better solution? The condition for hiding the error message could
also be made stricter by introducing a new fwnode_link flag to mark links that
have been moved by __fw_devlink_pickup_dangling_consumers().

Best regards,
Matthias


> 
> Fixes: ac66c5bbb437 ("driver core: Allow only unprobed consumers for SYNC_STATE_ONLY device links")
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
> Tested-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
> ---
>  drivers/base/core.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 2b4c0624b704..5eaafe3a280c 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2187,8 +2187,13 @@ static int fw_devlink_create_devlink(struct device *con,
>  		}
>  
>  		if (con != sup_dev && !device_link_add(con, sup_dev, flags)) {
> -			dev_err(con, "Failed to create device link (0x%x) with %s\n",
> -				flags, dev_name(sup_dev));
> +			if (flags & DL_FLAG_SYNC_STATE_ONLY &&
> +			    con->links.status != DL_DEV_NO_DRIVER &&
> +			    con->links.status != DL_DEV_PROBING)
> +				dev_dbg(con, "Skipping device link creation for probed device\n");
> +			else
> +				dev_err(con, "Failed to create device link (0x%x) with %s\n",
> +					flags, dev_name(sup_dev));
>  			ret = -EINVAL;
>  		}
>  
> 
> ---
> base-commit: b992b79ca8bc336fa8e2c80990b5af80ed8f36fd
> change-id: 20240624-fwdevlink-probed-no-err-45d21feb05fd
> 
> Best regards,

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