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

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Date:   Mon, 13 May 2019 11:06:39 +0100
From:   Måns Rullgård <mans@...sr.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Peter Chen <peter.chen@....com>,
        "linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-samsung-soc\@vger.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        "linux-kernel\@vger.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

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

> Hi Peter,
>
> On 2019-05-13 11:23, Peter Chen wrote:
>>> On 2019-05-13 11:00, Peter Chen wrote:
>>>>> 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.
>>>>>
>>>> Do you mind doing it at function exynos_ehci_get_phy of ehci-exynos.c?
>>> I don't mind fixing it in ehci-exynos, but frankly so far I have no
>>> idea how to do it.  The problem is that newly created USB devices
>>> get of-node pointer pointing to a node which if not intended for
>>> them. How this can be fixed in ehci-exynos?
>>>
>>   
>> Can't be workaround by setting of_node as NULL for EHCI controller or
>> for PHY node at exynos_ehci_get_phy?
>
> Ah, such workaround? I will check, but this will need to be done with 
> care, because have a side effect for other subsystems like regulators or 
> clocks.
>
> BTW, What's wrong with proper, full verification of USB device nodes?

Your approach so far doesn't address the actual problem of a conflict
between the generic USB DT bindings and those for the Exynos host
controller.  If you fix that, the validation issue goes away.

-- 
Måns Rullgård