linux-kernel - Re: [PATCH] xhci: Fix USB 3.1 enumeration issues by increasing roothub power-on-good delay

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Date:   Fri, 5 Nov 2021 21:56:59 +0200
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     stern@...land.harvard.edu, mr.yming81@...il.com,
        chunfeng.yun@...iatek.com, matthias.bgg@...il.com,
        nishadkamdar@...il.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, eddie.hung@...iatek.com
Subject: Re: [PATCH] xhci: Fix USB 3.1 enumeration issues by increasing
 roothub power-on-good delay

On 5.11.2021 18.15, Greg KH wrote:
> On Fri, Nov 05, 2021 at 06:00:36PM +0200, Mathias Nyman wrote:
>> Some USB 3.1 enumeration issues were reported after the hub driver removed
>> the minimum 100ms limit for the power-on-good delay.
>>
>> Since commit 90d28fb53d4a ("usb: core: reduce power-on-good delay time of
>> root hub") the hub driver sets the power-on-delay based on the
>> bPwrOn2PwrGood value in the hub descriptor.
>>
>> xhci driver has a 20ms bPwrOn2PwrGood value for both roothubs based
>> on xhci spec section 5.4.8, but it's clearly not enough for the
>> USB 3.1 devices, causing enumeration issues.
>>
>> Tests indicate full 100ms delay is needed.
>>
>> Reported-by: Walt Jr. Brake <mr.yming81@...il.com>
>> Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
> 
> So this needs:
> 	Fixes: 90d28fb53d4a ("usb: core: reduce power-on-good delay time of root hub")
> right?

I guess so, not sure on "Fixes" policy here.

This patch fixes an xhci issue revealed by ("usb: core: reduce power-on-good delay time of root hub")
That original patch itself looks correct, but these two patches should really go together to
avoid any enumeration issues.  

Thanks
-Mathias