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

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Message-ID: <e7f32280-57ec-6298-1a5d-8d2d4dc26667@samsung.com>
Date:   Wed, 8 May 2019 15:49:22 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Måns Rullgård <mans@...sr.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

Hi

On 2019-05-08 13:46, Måns Rullgård wrote:
> 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.

Right, this will be a better approach. I've just checked the code and a 
simple check for 'compatible' property presence can be easily added in 
drivers/usb/core/of.c in usb_of_get_device_node() and 
usb_of_get_interface_node() functions.

The second check could be added in drivers/usb/core/hub.c in 
usb_new_device() - to ensure that the device's vid/pid matches of_node 
compatible string.

Is this okay? Or just add a latter one?

> 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.

So far we don't have any use case for adding devicetree nodes for usb 
devices under Exynos EHCI/OHCI hcd, so this shouldn't be a problem for now.

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