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

From: Måns Rullgård
Date: Wed May 08 2019 - 11:28:43 EST

Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> writes:

> Hi
> On 2019-05-08 13:46, Måns Rullgård wrote:
>> Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> 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@xxxxxxxxxxxxx>
>>> Fixes: 01fdf179f4b0 ("usb: core: skip interfaces disabled in devicetree")
>>> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>>> ---
>>> 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?

I'm not sure where the best place to check is. Someone else will have
to weigh in on that.

>> 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.

None that you know of, that is. Regardless, the bindings are
inconsistent, and that needs to be fixed.

Måns Rullgård