linux-kernel - Re: [PATCH] usb: misc: onboard_usb_hub: Don't defer probing for 'incomplete' DT nodes

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Date:   Tue, 20 Dec 2022 08:55:52 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Matthias Kaehlcke <mka@...omium.org>, Rob Herring <robh@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Douglas Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Stefan Wahren <stefan.wahren@...e.com>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>
Subject: Re: [PATCH] usb: misc: onboard_usb_hub: Don't defer probing for
 'incomplete' DT nodes

On Tue, Dec 20, 2022 at 12:45:01AM +0000, Matthias Kaehlcke wrote:
> Some boards have device tree nodes for USB hubs supported by the
> onboard_usb_hub driver, but the nodes don't have all properties
> needed for the driver to work properly (which is not necessarily
> an error in the DT). Currently _find_onboard_hub() returns
> -EPROBE_DEFER in such cases, which results in an unusable USB hub,
> since successive probes fail in the same way. Use the absence of
> the "vdd" supply as an indicator of such 'incomplete' DT nodes
> and return -ENODEV.
> 
> Fixes: 8bc063641ceb ("usb: misc: Add onboard_usb_hub driver")
> Reported-by: Stefan Wahren <stefan.wahren@...e.com>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
> 
>  drivers/usb/misc/onboard_usb_hub.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
> index d63c63942af1..2968da515016 100644
> --- a/drivers/usb/misc/onboard_usb_hub.c
> +++ b/drivers/usb/misc/onboard_usb_hub.c
> @@ -363,6 +363,15 @@ static struct onboard_hub *_find_onboard_hub(struct device *dev)
>  	hub = dev_get_drvdata(&pdev->dev);
>  	put_device(&pdev->dev);
>  
> +	/*
> +	 * Some boards have device tree nodes for USB hubs supported by this
> +	 * driver, but the nodes don't have all properties needed for the driver
> +	 * to work properly. Use the absence of the "vdd" supply as an indicator
> +	 * of such nodes.
> +	 */
> +	if (!of_get_property(pdev->dev.of_node, "vdd", NULL))
> +		return ERR_PTR(-ENODEV);

Does this not break your original use case? Don't you want "vdd-supply"
here?

That said, this seems like the wrong property to look for both in
principle and as it is described as optional by the binding:

	Documentation/devicetree/bindings/usb/realtek,rts5411.yaml

It seems that you should use the compatible property and check that it
holds one of the expected values:

 - usbbda,5411
 - usbbda,411

rather than treat every hub node as describing a realtek hub (AFAIK,
there is no generic binding for this yet).

> +
>  	/*
>  	 * The presence of drvdata ('hub') indicates that the platform driver
>  	 * finished probing. This handles the case where (conceivably) we could

Johan