[PATCH] usb: core: improve handling of hubs with no ports

[Heiner Kallweit]

On 23.02.2022 03:10, Alan Stern wrote:
> On Tue, Feb 22, 2022 at 10:13:09PM +0100, Heiner Kallweit wrote:
>> I get the "hub doesn't have any ports" error message on a system with
>> Amlogic S905W SoC. Seems the SoC has internal USB 3.0 supports but
>> is crippled with regard to USB 3.0 ports.
>> Maybe we shouldn't consider this scenario an error. So let's change
>> the message to info level, but otherwise keep the handling of the
>> scenario as it is today. With the patch it looks like this on my
>> system.
>>
>> dwc2 c9100000.usb: supply vusb_d not found, using dummy regulator
>> dwc2 c9100000.usb: supply vusb_a not found, using dummy regulator
>> dwc2 c9100000.usb: EPs: 7, dedicated fifos, 712 entries in SPRAM
>> xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
>> xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 1
>> xhci-hcd xhci-hcd.0.auto: hcc params 0x0228f664 hci version 0x100 quirks 0x0000000002010010
>> xhci-hcd xhci-hcd.0.auto: irq 49, io mem 0xc9000000
>> hub 1-0:1.0: USB hub found
>> hub 1-0:1.0: 2 ports detected
>> xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
>> xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 2
>> xhci-hcd xhci-hcd.0.auto: Host supports USB 3.0 SuperSpeed
>> usb usb2: We don't know the algorithms for LPM for this host, disabling LPM.
>> hub 2-0:1.0: USB hub found
>> hub 2-0:1.0: hub has no ports, exiting
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1 at gmail.com>
>> ---
>>  drivers/usb/core/hub.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index 83b5aff25..e3f40d1f4 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -1423,9 +1423,8 @@ static int hub_configure(struct usb_hub *hub,
>>  		ret = -ENODEV;
>>  		goto fail;
>>  	} else if (hub->descriptor->bNbrPorts == 0) {
>> -		message = "hub doesn't have any ports!";
>> -		ret = -ENODEV;
>> -		goto fail;
>> +		dev_info(hub_dev, "hub has no ports, exiting\n");
>> +		return -ENODEV;
>>  	}
>>  
>>  	/*
> 
> How about instead changing xhci-hcd so that it doesn't try to register 
> a USB-3 root hub if the controller doesn't have any USB-3 ports?  I 
> think that would make more sense.
> 
Right, this would be better. I checked and it seems to be a little bit
bigger endeavor. If I let register_root_hub() fail, then this removes
the USB3 bus/host (shared hcd), but also the USB2 bus/host.
It took an additional change to xhci_plat_probe() to make it work on my
system. Not sure what the impact could be on systems not using
xhci_plat_probe(). Users may face the same issue like me, and having
a USB3 hub with no ports may remove also the USB2 bus/host.

What I can do: submit my patches as RFC, then there's a better basis
for a discussion.

> Alan Stern

Heiner