Re: [PATCH v2] usb: core: reduce power-on-good delay time of root hub

From: "Walt Jr. Brake" <mr.yming81@gmail.com>
To: Mathias Nyman <mathias.nyman@linux.intel.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Mathias Nyman <mathias.nyman@intel.com>
Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Nishad Kamdar <nishadkamdar@gmail.com>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	Eddie Hung <eddie.hung@mediatek.com>
Subject: Re: [PATCH v2] usb: core: reduce power-on-good delay time of root hub
Date: Wed, 3 Nov 2021 04:29:01 +0800	[thread overview]
Message-ID: <62d0ac30-f2b9-f58c-cb1e-215ccb455753@gmail.com> (raw)
In-Reply-To: <3cf46eaf-5443-30df-6d72-b92a6a518afc@linux.intel.com>

On 2/11/2021 17:05, Mathias Nyman wrote:
> On 1.11.2021 16.06, Alan Stern wrote:
>> On Sat, Oct 30, 2021 at 12:49:37PM +0800, Walt Jr. Brake wrote:
>>> This patch make USB 3.1 device cannot be detected, and I report the bug [1]
>>> to archlinux three month ago. Yesterday I try to fix it myself, and after I
>>> revert this patch, compile the kernel and test, it works.
>>>
>>> [1] https://bugs.archlinux.org/task/71660?project=1&pagenum=2
>>>
>>>
>>> diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
>>> index 22ea1f4f2d66..73f4482d833a 100644
>>> --- a/drivers/usb/core/hub.h
>>> +++ b/drivers/usb/core/hub.h
>>> @@ -148,10 +148,8 @@ static inline unsigned hub_power_on_good_delay(struct
>>> usb_hub *hub)
>>>   {
>>>          unsigned delay = hub->descriptor->bPwrOn2PwrGood * 2;
>>>
>>> -       if (!hub->hdev->parent) /* root hub */
>>> -               return delay;
>>> -       else /* Wait at least 100 msec for power to become stable */
>>> -               return max(delay, 100U);
>>> +       /* Wait at least 100 msec for power to become stable */
>>> +       return max(delay, 100U);
>>>   }
>> Mathias:
>>
>> It looks like the bPwrOn2PwrGood value in xhci-hcd's hub descriptor is
>> too small for some USB 3.1 devices.
>>
>> Can you look into this?
>>
>> Alan Stern
>>
> At first glance the xhci roothub bPwrOn2PwrGood value looks ok.
> xhci spec 5.4.8 states software should wait 20ms after asserting PP, before
> attempting to change the state of the port.
>
> xhci driver sets desc->bPwrOn2PwrGood = 10; (2ms interval, so equals 20ms )
>
> We should probably get this working immediately, so maybe revert that patch
> while looking into the rootcause.
>
> Walt Jr. Brake, instead of reverting that patch, could you test if changing the
> xhci roothub bPwrOn2PwrGood value helps.
>
> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> index a3f875eea751..756231a55602 100644
> --- a/drivers/usb/host/xhci-hub.c
> +++ b/drivers/usb/host/xhci-hub.c
> @@ -257,7 +257,7 @@ static void xhci_common_hub_descriptor(struct xhci_hcd *xhci,
>   {
>          u16 temp;
>   
> -       desc->bPwrOn2PwrGood = 10;      /* xhci section 5.4.9 says 20ms max */
> +       desc->bPwrOn2PwrGood = 50;      /* The 20ms in xhci 5.4.8 isn't enough for USB 3.1 */
>          desc->bHubContrCurrent = 0;
>   
>          desc->bNbrPorts = ports;
>
> Thanks
> -Mathias

Mathias:

Sorry to reply lately. I test with your patch, it works.

I also test with setting bPwrOn2PwrGood to 45, and it not work.

Seems that the minimal value should be 50 for this case.