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

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Message-ID: <5d0abe9c-613c-d39b-6746-78e5e5c2bbc5@samsung.com>
Date:   Mon, 13 May 2019 12:03:18 +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 2019-05-13 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?

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