linux-kernel - Re: [PATCH] usb: xhci: add support for performing fake doorbell

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Date:   Sat, 8 Oct 2016 20:28:40 -0500
From:   Rob Herring <robh@...nel.org>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Rafał Miłecki <rafal@...ecki.pl>,
        Mark Rutland <mark.rutland@....com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        "open list:USB SUBSYSTEM" <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: xhci: add support for performing fake doorbell

On Sat, Oct 01, 2016 at 11:58:10PM +0200, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@...ecki.pl>
> 
> Broadcom's Northstar XHCI controllers seem to need a special start
> procedure to work correctly. There isn't any official documentation on
> this, the problem is that controller doesn't detect any connected
> devices with default setup. Moreover connecting USB device to controller
> that doesn't run properly can cause SoC's watchdog issues.
> 
> A workaround that was successfully tested on multiple devices is to
> perform a fake doorbell. This patch adds code for doing that and a DT
> binding enabling it.
> 
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
>  Documentation/devicetree/bindings/usb/usb-xhci.txt |  2 +
>  drivers/usb/host/xhci-plat.c                       |  6 +++
>  drivers/usb/host/xhci.c                            | 63 ++++++++++++++++++++--
>  drivers/usb/host/xhci.h                            |  1 +
>  4 files changed, 69 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/usb/usb-xhci.txt b/Documentation/devicetree/bindings/usb/usb-xhci.txt
> index 966885c..ce01b7f 100644
> --- a/Documentation/devicetree/bindings/usb/usb-xhci.txt
> +++ b/Documentation/devicetree/bindings/usb/usb-xhci.txt
> @@ -26,6 +26,8 @@ Required properties:
>  Optional properties:
>    - clocks: reference to a clock
>    - usb3-lpm-capable: determines if platform is USB3 LPM capable
> +  - usb3-fake-doorbell: determines if controller requires a fake doorbell when
> +			starting it

You should use Northstar XHCI compatible string to enable this. Then the 
DT doesn't need updating.

Rob