linux-kernel - Re: [PATCH v2] usb: host: xhci: Avoid XHCI resume delay if SSUSB device is not present

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Message-ID: <ee47814e-969b-a96c-9323-e47bbf89297e@quicinc.com>
Date:   Mon, 11 Sep 2023 17:15:34 -0700
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <quic_jackp@...cinc.com>
Subject: Re: [PATCH v2] usb: host: xhci: Avoid XHCI resume delay if SSUSB
 device is not present

Hi Mathias,

On 9/11/2023 6:50 AM, Mathias Nyman wrote:
> On 1.9.2023 3.15, Wesley Cheng wrote:
>> There is a 120ms delay implemented for allowing the XHCI host 
>> controller to
>> detect a U3 wakeup pulse.  The intention is to wait for the device to 
>> retry
>> the wakeup event if the USB3 PORTSC doesn't reflect the RESUME link 
>> status
>> by the time it is checked.  As per the USB3 specification:
>>
>>    tU3WakeupRetryDelay ("Table 7-12. LTSSM State Transition Timeouts")
>>
>> This would allow the XHCI resume sequence to determine if the root hub
>> needs to be also resumed.  However, in case there is no device connected,
>> or if there is only a HSUSB device connected, this delay would still 
>> affect
>> the overall resume timing.
>>
>> Since this delay is solely for detecting U3 wake events (USB3 specific)
>> then ignore this delay for the disconnected case and the HSUSB connected
>> only case.
> 
> Thanks, makes sense
> 
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>> ---
>>   drivers/usb/host/xhci.c | 26 +++++++++++++++++++++++++-
>>   1 file changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
>> index e1b1b64a0723..640db6a4e686 100644
>> --- a/drivers/usb/host/xhci.c
>> +++ b/drivers/usb/host/xhci.c
>> @@ -805,6 +805,24 @@ static void xhci_disable_hub_port_wake(struct 
>> xhci_hcd *xhci,
>>       spin_unlock_irqrestore(&xhci->lock, flags);
>>   }
>> +static bool xhci_usb3_dev_connected(struct xhci_hcd *xhci)
>> +{
>> +    struct xhci_port    **ports;
>> +    int            port_index;
>> +    u32            portsc;
>> +
>> +    port_index = xhci->usb3_rhub.num_ports;
>> +    ports = xhci->usb3_rhub.ports;
>> +
>> +    while (port_index--) {
>> +        portsc = readl(ports[port_index]->addr);
>> +        if (portsc & (portsc & PORT_CONNECT))
>> +            return true;
>> +    }
>> +
>> +    return false;
>> +}
>> +
> 
> This is one way, but we can probably avoid re-reading all the usb3 
> portsc registers
> by checking if any bit is set in either:
> 
>   // bitfield, set if xhci usb3 port neatly set to U3 with a hub request
> xhci->usb3_rhub.bus_state.suspended_ports
> 
> // bitfield, set if xhci usb3 port is forced to U3 during xhci suspend.
> xhci->usb3_rhub.bus_state.bus_suspended
> 
> But haven't checked this works in all corner cases.
> 
Thanks for the suggestion.  I think I also looked at seeing if we could 
use the suspended_ports param, and it was missing one of the use cases 
we had.  I haven't thought on combining it with the bus_suspend param 
also to see if it could work.  Let me give it a try, and I'll get back 
to you.

Thanks
Wesley Cheng