linux-kernel - RE: [PATCH v2] usb: hub: try old enumeration scheme first for high speed devices

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Date:   Mon, 20 Aug 2018 01:59:11 +0000
From:   "Zengtao (B)" <prime.zeng@...ilicon.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
        "drinkcat@...omium.org" <drinkcat@...omium.org>,
        "felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>,
        "drake@...lessm.com" <drake@...lessm.com>,
        "mike.looijmans@...ic.nl" <mike.looijmans@...ic.nl>,
        "joe@...ches.com" <joe@...ches.com>,
        "Jonathan Corbet" <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Marc Zyngier" <marc.zyngier@....com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Thymo van Beers <thymovanbeers@...il.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: RE: [PATCH v2] usb: hub: try old enumeration scheme first for high
 speed devices

Hi Alan:

Thanks for your reply.

>-----Original Message-----
>From: Alan Stern [mailto:stern@...land.harvard.edu]
>Sent: Friday, August 17, 2018 10:19 PM
>To: Zengtao (B) <prime.zeng@...ilicon.com>
>Cc: gregkh@...uxfoundation.org; mathias.nyman@...ux.intel.com;
>drinkcat@...omium.org; felipe.balbi@...ux.intel.com;
>drake@...lessm.com; mike.looijmans@...ic.nl; joe@...ches.com;
>Jonathan Corbet <corbet@....net>; Thomas Gleixner <tglx@...utronix.de>;
>Ingo Molnar <mingo@...nel.org>; Rafael J. Wysocki
><rafael.j.wysocki@...el.com>; Marc Zyngier <marc.zyngier@....com>;
>Kai-Heng Feng <kai.heng.feng@...onical.com>; Thymo van Beers
><thymovanbeers@...il.com>; Frederic Weisbecker <frederic@...nel.org>;
>Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>; David Rientjes
><rientjes@...gle.com>; linux-doc@...r.kernel.org;
>linux-kernel@...r.kernel.org; linux-usb@...r.kernel.org
>Subject: Re: [PATCH v2] usb: hub: try old enumeration scheme first for high
>speed devices
>
>On Fri, 17 Aug 2018, Zeng Tao wrote:
>
>> The new scheme is required just to support legacy low and full-speed
>> devices. For high speed devices, it will slower the enumeration speed.
>> So in this patch we try the "old" enumeration scheme first for high
>> speed devices, and this is what Windows does since Windows 8.
>>
>> Signed-off-by: Zeng Tao <prime.zeng@...ilicon.com>
>> ---
>> Changes in v2:
>> 1. As suggested by Alan, mention in the commit log that this change is
>> follow what the Window does.
>> 2. As suggested by Roger, update the kernel-parameter description.
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt | 3 ++-
>>  drivers/usb/core/hub.c                          | 5 ++++-
>>  2 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt
>> b/Documentation/admin-guide/kernel-parameters.txt
>> index 533ff5c..95db23c 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -4453,7 +4453,8 @@
>>
>>  	usbcore.old_scheme_first=
>>  			[USB] Start with the old device initialization
>> -			scheme (default 0 = off).
>> +			scheme,  applies only to low and full-speed devices
>> +			 (default 0 = off).
>>
>>  	usbcore.usbfs_memory_mb=
>>  			[USB] Memory limit (in MB) for buffers allocated by diff --git
>> a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index
>> 1fb2668..d265b19 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -2661,10 +2661,13 @@ static bool use_new_scheme(struct
>usb_device *udev, int retry,
>>  	int old_scheme_first_port =
>>  		port_dev->quirks & USB_PORT_QUIRK_OLD_SCHEME;
>>
>> +	int quick_enumeration = (udev->speed == USB_SPEED_HIGH);
>
Okey, will fix in v3

>Minor style point: the preceding blank line should be eliminated.
>
>> +
>>  	if (udev->speed >= USB_SPEED_SUPER)
>>  		return false;
>>
>> -	return USE_NEW_SCHEME(retry, old_scheme_first_port ||
>old_scheme_first);
>> +	return USE_NEW_SCHEME(retry, old_scheme_first_port ||
>old_scheme_first
>> +			      || quick_enumeration);
>>  }
>>
>>  /* Is a USB 3.0 port in the Inactive or Compliance Mode state?
>
>Aside from that:
>
>Acked-by: Alan Stern <stern@...land.harvard.edu>

Okay , tag will be applied in v3.