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: <44b07e90-a9de-ea99-25c6-dc72cf39bbe1@ti.com>
Date:   Thu, 31 Oct 2019 12:35:28 +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

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);
>> +		writel(USB_CONF_USB3DIS, &priv_dev->regs->usb_conf);
>> +		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.

Pawel,

could you please confirm what is the best way to undo the high-speed
limit?

-- 
cheers,
-roger
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki