linux-kernel - Re: [PATCH v3] usb: core: verify devicetree nodes for USB devices

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Date:   Fri, 10 May 2019 11:43:41 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Peter Chen <peter.chen@....com>,
        Måns Rullgård <mans@...sr.com>
Cc:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        "linux-kernel@...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 v3] usb: core: verify devicetree nodes for USB devices

Hi Peter,

On 2019-05-10 05:10, Peter Chen wrote:
>
>> Marek Szyprowski <m.szyprowski@...sung.com> writes:
>>> Commit 69bec7259853 ("USB: core: let USB device know device node")
>>> added support for attaching devicetree node for USB devices. The
>>> mentioned commit however identifies the given USB device node only by the 'reg'
>>> property in the host controller children nodes. The USB device node
>>> however also has to have a 'compatible' property as described in
>>> Documentation/devicetree/bindings/usb/usb-device.txt. Lack for the
>>> 'compatible' property check might result in assigning a devicetree
>>> node, which is not intended to be the proper node for the given USB device.
>>>
>>> This is important especially when USB host controller has 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. Those binding
>>> predates support for USB devicetree nodes.
>>>
>>> Checking for the proper compatibility string allows to mitigate the
>>> conflict between USB device devicetree nodes and the bindings for USB
>>> controllers with child nodes. It also fixes the side-effect of the
>>> other commits, like 01fdf179f4b0 ("usb: core: skip interfaces disabled
>>> in devicetree"), which incorrectly disables some devices on Exynos
>>> based boards.
> Hi Marek,
>
> The purpose of your patch is do not set of_node for device under USB controller, right?

Right.

> I do not understand how 01fdf179f4b0 affect your boards, some nodes under
> the USB controller with status is not "okay", but still want to be enumerated?

Please look at the ehci node in arch/arm/boot/dts/exynos4.dtsi and then 
at the changes to that node in arch/arm/boot/dts/exynos4412-odroidx.dts. 
Exynos EHCI controller has 3 subnodes, which matches to the physical 
ports of it and allows the driver to enable given PHY ports depending on 
which physical port is used on the particular board. All ports cannot 
not be enabled by default, because PHY controller has limited resources 
and shares them between USB host and USB device ports.


Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland