linux-kernel - Re: [PATCH v3] usb: hub: try old enumeration scheme first for high speed devices

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Message-ID: <535e6c93-4369-c01e-953c-35e7041129e8@ti.com>
Date:   Mon, 20 Aug 2018 09:55:49 +0300
From:   Roger Quadros <rogerq@...com>
To:     Zeng Tao <prime.zeng@...ilicon.com>, <gregkh@...uxfoundation.org>,
        <stern@...land.harvard.edu>, <mathias.nyman@...ux.intel.com>,
        <drinkcat@...omium.org>, <felipe.balbi@...ux.intel.com>,
        <drake@...lessm.com>, <ravisadineni@...omium.org>,
        <joe@...ches.com>
CC:     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>,
        Mike Looijmans <mike.looijmans@...ic.nl>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v3] usb: hub: try old enumeration scheme first for high
 speed devices

On 20/08/18 13:04, 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>

You need to add Alan's Ack here. I don't think you need to resend though.

Reviewed-by: Roger Quadros <rogerq@...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.
> 
> Changes in v3:
> 1. Remove the blank line suggested by Alan.
> 2. Tag applied.
> 
> Acked-by: Alan Stern <stern@...land.harvard.edu>
> Signed-off-by: Zeng Tao <prime.zeng@...ilicon.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 3 ++-
>  drivers/usb/core/hub.c                          | 4 +++-
>  2 files changed, 5 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..003fac0 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2660,11 +2660,13 @@ 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);
>  
>  	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?
> 

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