Re: [RFC][PATCH 2/2] usb: dwc2: Add a quirk to allow speed negotiation for Hisilicon Hi6220

[John Youn]

On 10/20/2016 5:43 PM, Chen Yu wrote:
> On 2016/10/19 6:21, John Youn wrote:
>> On 10/16/2016 7:42 PM, Chen Yu wrote:
>>>
>>>
>>> On 2016/10/15 3:37, John Youn wrote:
>>>> On 10/13/2016 4:36 PM, John Stultz wrote:
>>>>> From: Chen Yu <chenyu56@xxxxxxxxxx>
>>>>>
>>>>> The Hi6220's usb controller is limited in that it does not
>>>>> automatically autonegotiate the usb speed. Thus it requires a
>>>>> quirk so that we can manually negotiate the best usb speed for
>>>>> the attached device.
>>>>
>>>> Hi,
>>>>
>>>> Could you expand more on this by explaining what exactly is the
>>>> limitation and the workaround?
>>>>
>>>
>>> The USB host limitation of Hisilicon Hi6220 is full-speed and low-speed
>>> devices can not be enumerated when gets plugged behind a hub.
>>>
>>>> [snip]
>>>>
>>>>> +/*
>>>>> + * HPRT0_SPD_HIGH_SPEED: high speed
>>>>> + * HPRT0_SPD_FULL_SPEED: full speed
>>>>> + */
>>>>> +static void dwc2_change_bus_speed(struct usb_hcd *hcd, int speed)
>>>>> +{
>>>>> +	struct dwc2_hsotg *hsotg = dwc2_hcd_to_hsotg(hcd);
>>>>> +
>>>>> +	if (hsotg->core_params->speed == speed)
>>>>> +		return;
>>>>> +
>>>>> +	hsotg->core_params->speed = speed;
>>>>> +	queue_work(hsotg->wq_otg, &hsotg->wf_otg);
>>>>> +}
>>>>> +
>>>>> +static int dwc2_alloc_dev(struct usb_hcd *hcd, struct usb_device *udev)
>>>>> +{
>>>>> +	struct dwc2_hsotg *hsotg = dwc2_hcd_to_hsotg(hcd);
>>>>> +
>>>>> +	if (!hsotg->change_speed_quirk)
>>>>> +		return 1;
>>>>> +
>>>>> +	hsotg->device_count++;
>>>>
>>>> Why do you need to track the device count?
>>>>
>>>>> +	dev_info(hsotg->dev, "Device count is %u after alloc dev\n",
>>>>> +			hsotg->device_count);
>>>>> +
>>>>> +	return 1;
>>>>> +}
>>>>> +
>>>>> +static void dwc2_free_dev(struct usb_hcd *hcd, struct usb_device *udev)
>>>>> +{
>>>>> +	struct dwc2_hsotg *hsotg = dwc2_hcd_to_hsotg(hcd);
>>>>> +
>>>>> +	if (!hsotg->change_speed_quirk)
>>>>> +		return;
>>>>> +
>>>>> +	if (hsotg->device_count)
>>>>> +		hsotg->device_count--;
>>>>> +
>>>>> +	dev_info(hsotg->dev, "Device count is %u after free dev\n",
>>>>> +			hsotg->device_count);
>>>>> +
>>>>> +	if (hsotg->device_count == 1 && udev->parent &&
>>>>> +			udev->parent->speed > USB_SPEED_UNKNOWN &&
>>>>> +			udev->parent->speed < USB_SPEED_HIGH) {
>>>>> +		dev_info(hsotg->dev, "Set speed to default high-speed\n");
>>>>> +		dwc2_change_bus_speed(hcd, HPRT0_SPD_HIGH_SPEED);
>>>>> +	}
>>>>> +}
>>>>> +
>>>>> +static int dwc2_reset_device(struct usb_hcd *hcd, struct usb_device *udev)
>>>>> +{
>>>>> +	struct dwc2_hsotg *hsotg = dwc2_hcd_to_hsotg(hcd);
>>>>> +
>>>>> +	if (!hsotg->change_speed_quirk)
>>>>> +		return 0;
>>>>> +
>>>>> +	if (udev->speed == USB_SPEED_HIGH) {
>>>>> +		dev_info(hsotg->dev, "Set speed to high-speed\n");
>>>>> +		dwc2_change_bus_speed(hcd, HPRT0_SPD_HIGH_SPEED);
>>>>> +	} else if (udev->speed == USB_SPEED_FULL
>>>>> +			|| udev->speed == USB_SPEED_LOW) {
>>>>> +		dev_info(hsotg->dev, "Set speed to full-speed\n");
>>>>> +		dwc2_change_bus_speed(hcd, HPRT0_SPD_FULL_SPEED);
>>>>> +	}
>>>>
>>>> It seems you are reinitializing the core every time a device is reset
>>>> and the udev->speed does not match the core_param speed. But how is
>>>> the udev->speed being set correctly if the hw cannot negotiate the
>>>> speed in the first place?
>>>>
>>>
>>> The hardware can negotiate the speed, but communication with a full-speed or
>>> low-speed device behind a hub is the problem.
>>>
>>>> Also should it be for every device? What about if a device gets
>>>> plugged in behind a hub? I don't think you want to execute this code
>>>> in that case.
>>>>
>>>> This should only affect devices plugged into the root hub, correct?
>>>> And the hsotg controller only has one root hub port. It seems things
>>>> could be simplified a bit.
>>>>
>>>
>>> The patch is initially written for Hikey Hi6220 board, and there is a
>>> hub always connected to root hub, so the patch sets the configuration to
>>> HPRT0_SPD_HIGH_SPEED when there is only one device(the hub).
>>
>> Ok, I see.
>>
>>>
>>> Thanks for your suggestions, the patch needs modified in these aspect:
>>> 1. Change the speed setting only when the device is behind a hub in dwc2_reset_device.
>>
>> I still think you will have issues with multiple devices. Since you
>> have a built-in hub after root hub, it will always be behind the
>> hub. So whenver you need to change speeds, it will always reset every
>> device in the tree. Have you tested with multiple devices and also
>> multiple levels of hubs?
>>
> 
> Yes, a full-speed device or low-speed device being plugged in will reset other devices
> if current speed setting is not full-speed.
> I have tested with multiple devices and also two levels of high-speed hubs,
> the patch was working well for enumerating full-speed device and low-speed device.
> Also it changed the speed to high when there was only one hub connected to root hub.
> 
> 
>>> 2. Change the speed to HPRT0_SPD_HIGH_SPEED only when the last device is a hub.
>>>
>>> What do you think about the fix? Any suggestions will be appreciate!
>>
>> I'm not sure if any fix can work for all cases. Has this problem
>> always been there?
> 
> Yes, the problem is always there because Hi6220 can not support "Split Transaction".

So the problem is actually that the on board hub doesn't support
splits? That's much different than your initial description and the
workaround makes more sense in this context.

But why can't it support splits?

And how can an FS device pass enumeration if the hub doesn't support
splits? I feel like there is still something missing.

Also, if you plug in a HS hub, and then an FS device behind that. That
should work fine, no? So you wouldn't want to reset anything in that
case.

Regards,
John