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When disconnecting a USB hub that has some child device(s) connected to it (such as a USB mouse), then the stack tries to clear halt and reset device(s) which are _already_ physically disconnected. The issue has been reproduced with: CPU: IMX6D5EYM10AD or MCIMX6D5EYM10AE. SW: U-Boot 2019.07 and kernel 4.19.40. CPU: HP Proliant Microserver Gen8. SW: Linux version 4.2.3-300.fc23.x86_64 In this situation there will be error bit for MMF active yet the CERR equals EHCI_TUNE_CERR + halt. Existing implementation interprets this as a stall [1] (chapter 8.4.5). The possible conditions when the MMF will be active + halt can be found from [2] (Table 4-13). Fix for the issue is to check whether MMF is active and PID Code is IN before checking for the stall. If these conditions are true then it is not a stall. What happens after the fix is that when disconnecting a hub with attached device(s) the situation is not interpret as a stall. [1] [https://www.usb.org/document-library/usb-20-specification, usb_20.pdf] [2] [https://www.intel.com/content/dam/www/public/us/en/documents/ technical-specifications/ehci-specification-for-usb.pdf] Signed-off-by: Erkka Talvitie <erkka.talvitie@vincit.fi> Reviewed-by: Alan Stern <stern@rowland.harvard.edu> Cc: stable <stable@vger.kernel.org> Link: https://lore.kernel.org/r/ef70941d5f349767f19c0ed26b0dd9eed8ad81bb.1576050523.git.erkka.talvitie@vincit.fi Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.