linux-kernel - Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

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Date:   Mon, 17 Oct 2016 23:21:14 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Hauke Mehrtens <hauke@...ke-m.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rafał Miłecki <rafal@...ecki.pl>,
        Florian Fainelli <florian@...nwrt.org>
Subject: Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

On 17 October 2016 at 23:10, Hauke Mehrtens <hauke@...ke-m.de> wrote:
> On 10/17/2016 10:30 PM, 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 of
>> 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 this and enables
>> it on BCM4708 family.
>>
>> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
>> ---
>> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated binding
>>     for it. Thanks Rob for your comment on this.
>> ---
>>  drivers/usb/host/xhci-plat.c |  6 +++++
>>  drivers/usb/host/xhci.c      | 63 +++++++++++++++++++++++++++++++++++++++++---
>>  drivers/usb/host/xhci.h      |  1 +
>>  3 files changed, 67 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
>> index ed56bf9..b01a3be 100644
>> --- a/drivers/usb/host/xhci-plat.c
>> +++ b/drivers/usb/host/xhci-plat.c
>> @@ -56,12 +56,18 @@ static int xhci_priv_init_quirk(struct usb_hcd *hcd)
>>
>>  static void xhci_plat_quirks(struct device *dev, struct xhci_hcd *xhci)
>>  {
>> +     struct platform_device  *pdev = to_platform_device(dev);
>> +     struct device_node      *node = pdev->dev.of_node;
>> +
>>       /*
>>        * As of now platform drivers don't provide MSI support so we ensure
>>        * here that the generic code does not try to make a pci_dev from our
>>        * dev struct in order to setup MSI
>>        */
>>       xhci->quirks |= XHCI_PLAT;
>> +
>> +     if (node && of_machine_is_compatible("brcm,bcm4708"))
>> +             xhci->quirks |= XHCI_FAKE_DOORBELL;
>
> Are you sure only the bcm4708 and similar SoCs are affected? Having here
> a list with 3 or more checks would looks strange. I prefer your first patch.
>
> @Florian do you know if other Broadcom SoC are affected by this problem
> or are only Northstar SoCs affected?

I also believed usb3-fake-doorbell property looks nicer, but then just
followed Rob's suggestion.

I don't know about Northstar Plus or Northstar 2, I just know it's not
needed for BCM53573.

-- 
Rafał