netdev - Re: [PATCH v2] r8152: check disconnect status after long sleep

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Date:   Sat, 29 Feb 2020 21:20:35 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     vicamo@...il.com
Cc:     grundler@...omium.org, hayeswang@...ltek.com,
        kai.heng.feng@...onical.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org, pmalani@...omium.org,
        vicamo.yang@...onical.com
Subject: Re: [PATCH v2] r8152: check disconnect status after long sleep

From: You-Sheng Yang <vicamo@...il.com>
Date: Wed, 26 Feb 2020 23:37:10 +0800

> From: You-Sheng Yang <vicamo.yang@...onical.com>
> 
> Dell USB Type C docking WD19/WD19DC attaches additional peripherals as:
> 
>   /: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/6p, 5000M
>       |__ Port 1: Dev 11, If 0, Class=Hub, Driver=hub/4p, 5000M
>           |__ Port 3: Dev 12, If 0, Class=Hub, Driver=hub/4p, 5000M
>           |__ Port 4: Dev 13, If 0, Class=Vendor Specific Class,
>               Driver=r8152, 5000M
> 
> where usb 2-1-3 is a hub connecting all USB Type-A/C ports on the dock.
> 
> When hotplugging such dock with additional usb devices already attached on
> it, the probing process may reset usb 2.1 port, therefore r8152 ethernet
> device is also reset. However, during r8152 device init there are several
> for-loops that, when it's unable to retrieve hardware registers due to
> being disconnected from USB, may take up to 14 seconds each in practice,
> and that has to be completed before USB may re-enumerate devices on the
> bus. As a result, devices attached to the dock will only be available
> after nearly 1 minute after the dock was plugged in:
 ...
> To solve this long latency another test to RTL8152_UNPLUG flag should be
> added after those 20ms sleep to skip unnecessary loops, so that the device
> probe can complete early and proceed to parent port reset/reprobe process.
> 
> This can be reproduced on all kernel versions up to latest v5.6-rc2, but
> after v5.5-rc7 the reproduce rate is dramatically lowered to 1/30 or less
> while it was around 1/2.
> 
> Signed-off-by: You-Sheng Yang <vicamo.yang@...onical.com>

Applied, thank you.