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From: Roger Quadros <rogerq@ti.com>
To: Zeng Tao <prime.zeng@hisilicon.com>, <gregkh@linuxfoundation.org>,
	<stern@rowland.harvard.edu>, <mathias.nyman@linux.intel.com>,
	<drinkcat@chromium.org>, <felipe.balbi@linux.intel.com>,
	<drake@endlessm.com>, <mike.looijmans@topic.nl>,
	<joe@perches.com>
Cc: <linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] usb: hub: try old enumeration scheme first for high speed devices
Date: Fri, 10 Aug 2018 13:50:43 +0300	[thread overview]
Message-ID: <a29afa26-22b4-3188-f9ee-993e44df7703@ti.com> (raw)
In-Reply-To: <1533913304-15737-1-git-send-email-prime.zeng@hisilicon.com>

Hi,

On 10/08/18 18:01, 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.

How slow does it get? Is it significant?
Do we risk breaking existing HS devices that work? I don't think we can
be sure till we run this through testing.

> 
> Signed-off-by: Zeng Tao <prime.zeng@hisilicon.com>
> ---
>  drivers/usb/core/hub.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> 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);
> +
>  	if (udev->speed >= USB_SPEED_SUPER)
>  		return false;

how about replacing the above if with

	if (udev->speed >= USB_SPEED_HIGH)
		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);
>  }

Now we no longer respect the "old_scheme_first" parameter for most of the devices.

It should be clarified in Documentation/admin/kernel-parameters.txt that
"old_scheme_first" is only applicable to LOW/FULL speed devices.

>  
>  /* Is a USB 3.0 port in the Inactive or Compliance Mode state?
> 

-- 
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

  reply	other threads:[~2018-08-10 10:51 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-10 15:01 [PATCH] usb: hub: try old enumeration scheme first for high speed devices Zeng Tao
2018-08-10 10:50 ` Roger Quadros [this message]
2018-08-10 14:19   ` Alan Stern
2018-08-14  7:35     ` Zengtao (B)
2018-08-14 14:39       ` Alan Stern
2018-08-16  6:21         ` Zengtao (B)
2018-08-16  7:16           ` Roger Quadros
2018-08-16 10:59             ` Zengtao (B)
2018-08-16 11:13               ` Roger Quadros
2018-08-17  2:15                 ` Zengtao (B)
2018-08-14  7:33   ` Zengtao (B)
2018-08-16  7:31     ` Roger Quadros
2018-09-28 11:27 Zeng Tao

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