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: <86a7fbc4-136f-78bb-4677-784199842c9f@ti.com>
Date:   Thu, 31 Oct 2019 13:02:14 +0200
From:   Roger Quadros <rogerq@...com>
To:     Felipe Balbi <balbi@...nel.org>, <gregkh@...uxfoundation.org>,
        <pawell@...ence.com>
CC:     <peter.chen@....com>, <nsekhar@...com>, <kurahul@...ence.com>,
        <linux-usb@...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 31/10/2019 12:55, Felipe Balbi wrote:
> 
> 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.

> 
> 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