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: <03bb6f7e-5545-3047-d3f4-4fa9789d0bcb@ti.com>
Date:   Mon, 4 Nov 2019 11:18:33 +0200
From:   Roger Quadros <rogerq@...com>
To:     Pawel Laszczak <pawell@...ence.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



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?

> 
> 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.
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