linux-kernel - Re: [PATCH v2] usb: core: verify devicetree nodes for disabled interfaces

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Date:   Wed, 08 May 2019 12:46:33 +0100
From:   Måns Rullgård <mans@...sr.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     linux-usb@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Markus Reichl <m.reichl@...etechno.de>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH v2] usb: core: verify devicetree nodes for disabled interfaces

Marek Szyprowski <m.szyprowski@...sung.com> writes:

> Commit 01fdf179f4b0 ("usb: core: skip interfaces disabled in devicetree")
> add support for disabling given USB device interface by adding nodes to
> the USB host controller device. The mentioned commit however identifies
> the given USB interface node only by the 'reg' property in the host
> controller children nodes and then checks for their the 'status'. The USB
> device interface nodes however also has to have a 'compatible' property as
> described in Documentation/devicetree/bindings/usb/usb-device.txt. This is
> important, because USB host controller might have child-nodes for other
> purposes. For example, Exynos EHCI and OHCI drivers already define
> child-nodes for each physical root hub port and assigns respective PHY
> controller and parameters for them. This conflicts with the proposed
> approach and verifying for the presence of the compatible property fixes
> this issue without changing the bindings and the way the PHY controllers
> are handled by Exynos EHCI/OHCI drivers.
>
> Reported-by: Markus Reichl <m.reichl@...etechno.de>
> Fixes: 01fdf179f4b0 ("usb: core: skip interfaces disabled in devicetree")
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  drivers/usb/core/message.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> index e844bb7b5676..6f7d047392bd 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -2009,6 +2009,7 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
>  		struct usb_interface *intf = cp->interface[i];
>
>  		if (intf->dev.of_node &&
> +		    of_find_property(intf->dev.of_node, "compatible", NULL) &&
>  		    !of_device_is_available(intf->dev.of_node)) {
>  			dev_info(&dev->dev, "skipping disabled interface %d\n",
>  				 intf->cur_altsetting->desc.bInterfaceNumber);
> -- 

I don't think this is the right approach.  We don't want to be adding
such checks everywhere the of_node is used.  A better way might be to
not set of_node at all in the absence of a proper "compatible" string.

Then there's the problem of how to resolve the incompatibility between
the generic USB and Exynos bindings.  One possible fix could be to use
a child node of the controller node to represent the root hub.  Since
the driver currently doesn't work at all if a devicetree has nodes for
USB devices, there should be no compatibility concerns.

-- 
Måns Rullgård