linux-kernel - RE: [PATCH v2] usb: cdns3: gadget: Fix g_audio use case when connected to Super-Speed host

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Message-ID: <BYAPR07MB4709C1750988DBD0F4AC5FB9DD7F0@BYAPR07MB4709.namprd07.prod.outlook.com>
Date:   Mon, 4 Nov 2019 15:16:41 +0000
From:   Pawel Laszczak <pawell@...ence.com>
To:     Roger Quadros <rogerq@...com>, Felipe Balbi <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "peter.chen@....com" <peter.chen@....com>,
        "nsekhar@...com" <nsekhar@...com>,
        Rahul Kumar <kurahul@...ence.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] usb: cdns3: gadget: Fix g_audio use case when
 connected to Super-Speed host

Hi,

>
>On 03/11/2019 10:17, Pawel Laszczak wrote:
>> Hi,
>>
>>>>
>>>> Hi,
>>>>
>>>> Roger Quadros <rogerq@...com> writes:
>>>>
>>>>> Hi,
>>>>>
>>>>> On 31/10/2019 10:55, Felipe Balbi wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Roger Quadros <rogerq@...com> writes:
>>>>>>
>>>>>>> Take into account gadget driver's speed limit when programming
>>>>>>> controller speed.
>>>>>>>
>>>>>>> Fixes: commit 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
>>>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>>>>> Acked-by: Peter Chen <peter.chen@....com>
>>>>>>> ---
>>>>>>>
>>>>>>> Changelog:
>>>>>>> v2
>>>>>>> - Add Fixes line
>>>>>>>
>>>>>>>     drivers/usb/cdns3/gadget.c | 31 ++++++++++++++++++++++++++-----
>>>>>>>     1 file changed, 26 insertions(+), 5 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/usb/cdns3/gadget.c b/drivers/usb/cdns3/gadget.c
>>>>>>> index 40dad4e8d0dc..1c724c20d468 100644
>>>>>>> --- a/drivers/usb/cdns3/gadget.c
>>>>>>> +++ b/drivers/usb/cdns3/gadget.c
>>>>>>> @@ -2338,9 +2338,35 @@ static int cdns3_gadget_udc_start(struct usb_gadget *gadget,
>>>>>>>     {
>>>>>>>     	struct cdns3_device *priv_dev = gadget_to_cdns3_device(gadget);
>>>>>>>     	unsigned long flags;
>>>>>>> +	enum usb_device_speed max_speed = driver->max_speed;
>>>>>>>
>>>>>>>     	spin_lock_irqsave(&priv_dev->lock, flags);
>>>>>>>     	priv_dev->gadget_driver = driver;
>>>>>>> +
>>>>>>> +	/* limit speed if necessary */
>>>>>>> +	max_speed = min(driver->max_speed, gadget->max_speed);
>>>>>>> +
>>>>>>> +	switch (max_speed) {
>>>>>>> +	case USB_SPEED_FULL:
>>>>>>> +		writel(USB_CONF_SFORCE_FS, &priv_dev->regs->usb_conf);
>>>>
>>>> so this forces the controller to FS
>>>
>>> Right.
>>>
>>>>
>>>>>>> +		writel(USB_CONF_USB3DIS, &priv_dev->regs->usb_conf);
>>>>
>>>> and this disconnects in superspeed? What is this supposed to do?
>>>>
>>>
>>> It says "Disconnect USB device in SuperSpeed".
>>>
>>> We were asked to set that bit to limit it to HS.
>>>
>>>>>>> +		break;
>>>>>>> +	case USB_SPEED_HIGH:
>>>>>>> +		writel(USB_CONF_USB3DIS, &priv_dev->regs->usb_conf);
>>>>>>> +		break;
>>>>>>> +	case USB_SPEED_SUPER:
>>>>>>> +		break;
>>>>>>> +	default:
>>>>>>> +		dev_err(priv_dev->dev,
>>>>>>> +			"invalid maximum_speed parameter %d\n",
>>>>>>> +			max_speed);
>>>>>>> +		/* fall through */
>>>>>>> +	case USB_SPEED_UNKNOWN:
>>>>>>> +		/* default to superspeed */
>>>>>>> +		max_speed = USB_SPEED_SUPER;
>>>>>>> +		break;
>>>>>>> +	}
>>>>>>
>>>>>> I had suggested some simplification for this case statement.
>>>>>>
>>>>>
>>>>> oops, looks like Greg picked this already.
>>>>>
>>>>> During more tests today I just observed that this patch causes
>>>>> the following regression.
>>>>>
>>>>> Connect EVM to Super-Speed host
>>>>> Load g_audio. (this enumerates as HS which is fine)
>>>>> unload g_audio
>>>>> load g_zero (this enumerates at HS instead of SS).
>>>>>
>>>>> This is because the speed limit that we set doesn't get cleared.
>>>>>
>>>>> Now the bits are write only and there is a way to undo USB_CONF_SFORCE_FS
>>>>> by writing USB_CONF_CFORCE_FS, however there is no corresponding bit
>>>>> to clear USB_CONF_USB3DIS. Only way seems to be USB_CFG_SWRST which
>>>>> is a bit harsh IMO.
>>>>
>>>> Isn't bit 0 enough?
>>>>
>>>> /* Reset USB device configuration. */
>>>> #define USB_CONF_CFGRST		BIT(0)
>>>
>>> Probably not, as explanation of USB3DIS bit says,
>>> "To connect disconnected device, CPU performs
>>> software reset (CFG.SWRST)." which is bit 7. "Device software reset.
>>>
>>> But I'll let Pawel comment on this.
>>
>> Yes it's the only way to return back to SS mode.
>> The USB speed is detecting during connecting.
>> CFG.SWRST make reconnect.
>
>Can this be done as part of udc_start or udc_stop?

I think that it should work in both cases, however because it finish with connection 
so probably the better will be udc_start function. 

>
>>
>> Maybe it would be better to add SS support in g_audio function.
>
>Not every gadget needs SS, so this is not the right way IMO.
>
>>
>>>>
>>>> Also, now that I look at this more carefully, you should move that code
>>>> to udc_set_speed().
>>>>
>>>
>>> Agreed. I'll revise the implementation to move it to udc_set_speed()
>>> once I know how to undo the USB3DIS.
>>>
>
>
>--
>cheers,
>-roger
>Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
>Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki