linux-kernel - USB disk speed regression WD Elements - with bisect result 22547c4cc4fe20698a6a85a55b8788859134b8e4

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Date:   Mon, 24 Jul 2017 14:03:35 +0200
From:   Zdenek Kabelac <zkabelac@...hat.com>
To:     LKML <linux-kernel@...r.kernel.org>, dianders@...omium.org,
        linux@...ck-us.net, stern@...land.harvard.edu,
        gregkh@...uxfoundation.org
Subject: USB disk speed regression WD Elements - with bisect result
 22547c4cc4fe20698a6a85a55b8788859134b8e4

Hi

I've problem with my USB storage devices:  WD Elements 1TB.
(Bus 004 Device 002: ID 1058:10a8 Western Digital Technologies, Inc. Elements 
Portable (WDBUZG))

After kernel >4.9  when disk is attached via cable it has very low speed 
(less then 1MB/s).

It can run at full speed (>22MB/s) when the Linux kernel is fully rebooted (so 
disk is attached during the reboot of Lenovo T61, C2D, Fedora Rawhide).

However when >4.9 kernel is running and disk is just attached it's very slow.

I've played a bisect game - and the clean result has been:

22547c4cc4fe20698a6a85a55b8788859134b8e4

When I just revert this patch with 4.13-rc1 - it's again running with full 
speed even when disk is attached (thus no reboot is needed for full speed).

So while I've no idea what 22547c4cc4fe20698... is doing, it seems to have 
some unpleasant side-effect on regular USB devices.

So what else is needed to get this properly working ?
(assuming plain revert of  22547c4cc4fe20698 is unwanted).

What more info can I provide to get this storage 'normally' usable without 
rebooting the machine.

Regards

Zdenek