linux-kernel - Re: [PATCH v2] fsl/usb: Workarourd for USB erratum-A005697

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Message-ID: <Pine.LNX.4.44L0.1611251008030.1509-100000@netrider.rowland.org>
Date:   Fri, 25 Nov 2016 10:13:53 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Changming Huang <jerry.huang@....com>
cc:     gregkh@...uxfoundation.org, <ramneek.mehresh@....com>,
        <julia.lawall@...6.fr>, <sriram.dash@....com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] fsl/usb: Workarourd for USB erratum-A005697

On Fri, 25 Nov 2016, Changming Huang wrote:

> The EHCI specification states the following in the SUSP bit description:
> In the Suspend state, the port is senstive to resume detection.
> Note that the bit status does not change untile the port is suspended and
> that there may be a delay in susupending a port if there is a transaction
> currently in progress on the USB.
> 
> However, in NXP USBDR controller, the PORTSCx[SUSP] bit changes immediately
> when the application sets it and not when the port is actually suspended.
> 
> So the application must wait for at least 10 milliseconds after a port
> indicates that it is suspended, to make sure this port has entered
> suspended state before initiating this port resume using the Force Port
> Resume bit. This bit is for NXP controller, not EHCI compatible.
> 
> Signed-off-by: Changming Huang <jerry.huang@....com>
> Signed-off-by: Ramneek Mehresh <ramneek.mehresh@....com>
> ---
> Change in v2:
> - move sleep out of spin-lock and add more comment for this workaround

This patch is incomplete.

> --- a/drivers/usb/host/ehci-hub.c
> +++ b/drivers/usb/host/ehci-hub.c
> @@ -310,6 +310,13 @@ static int ehci_bus_suspend (struct usb_hcd *hcd)
>  	}
>  	spin_unlock_irq(&ehci->lock);
>  
> +	if (changed && ehci_has_fsl_susp_errata(ehci))
> +		/* Wait for at least 10 millisecondes to ensure the controller
> +		 * enter the suspend status before initiating a port resume
> +		 * using the Fore Port Resume bit (Not-EHCI compatible).
> +		 */

The proper style for multi-line comments is:

		/*
		 * Wait for ...
		 * ...
		 */

Also, "Force" is misspelled.

> +		usleep_range(10000, 20000);
> +
>  	if ((changed && ehci->has_tdi_phy_lpm) || fs_idle_delay) {
>  		/*
>  		 * Wait for HCD to enter low-power mode or for the bus

The patch does not change the code around line 1190 in the original
file:

			/* After above check the port must be connected.
			 * Set appropriate bit thus could put phy into low power
			 * mode if we have tdi_phy_lpm feature
			 */
			temp &= ~PORT_WKCONN_E;
			temp |= PORT_WKDISC_E | PORT_WKOC_E;
			ehci_writel(ehci, temp | PORT_SUSPEND, status_reg);

This code sets the PORT_SUSPEND bit but does not have a 10-ms delay.  
You need to add a delay here.

Alan Stern