linux-kernel - Re: EHCI

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Date:   Fri, 17 Mar 2017 12:44:25 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Lipengcheng <lpc.li@...ilicon.com>
cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: EHCI 

On Fri, 17 Mar 2017, Lipengcheng wrote:

> Hi,
> In the ehci-hub.c,the ehci_handshake(ehci, status_reg, PORT_RESET, 0,
> 1000) use that the timeout is 1000us. The 1000us timeout can not
> satisfy all the chips. The EHCI protocol describes:A host controller
> must terminate the reset and stabilize the state of the port within 2
> milliseconds of software transitioning this bit from a one to a zero.
> So I think timeout time is set to 2000us more appropriate. If I set
> the timeout time is set to 2000us and may it produce side effects?

That is a long time to wait with interrupts disabled.  You probably 
should release the spinlock and enable interrupts during the handshake.

Have you seen any errors with the current 1000 us value?  If you 
haven't, there's no reason to change the code.

Alan Stern