Re: [PATCH v2 10/10] usb: dwc2/gadget: rework suspend/resume code to correctly restore gadget state

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

On 2014-10-25 03:16, Paul Zimmerman wrote:
>> From: Marek Szyprowski [mailto:m.szyprowski@samsung.com]
>> Sent: Monday, October 20, 2014 3:46 AM
>>
>> Suspend/resume code assumed that the gadget was always enabled and
>> connected to usb bus. This means that the actual state of the gadget
>> (soft-enabled/disabled or connected/disconnected) was not correctly
>> preserved on suspend/resume cycle. This patch fixes this issue.
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>> ---
>>   drivers/usb/dwc2/core.h   |  4 +++-
>>   drivers/usb/dwc2/gadget.c | 43 +++++++++++++++++++++++++++----------------
>>   2 files changed, 30 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h
>> index bf015ab3b44c..3648b76a18b4 100644
>> --- a/drivers/usb/dwc2/core.h
>> +++ b/drivers/usb/dwc2/core.h
>> @@ -210,7 +210,9 @@ struct s3c_hsotg {
>>   	u8                      ctrl_buff[8];
>>
>>   	struct usb_gadget       gadget;
>> -	unsigned int            setup;
>> +	unsigned int            setup:1;
>> +	unsigned int		connected:1;
>> +	unsigned int		enabled:1;
>>   	unsigned long           last_rst;
>>   	struct s3c_hsotg_ep     *eps;
>>   };
>> diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
>> index 0d34cfc71bfb..c6c6cf982c90 100644
>> --- a/drivers/usb/dwc2/gadget.c
>> +++ b/drivers/usb/dwc2/gadget.c
>> @@ -2925,6 +2925,8 @@ static int s3c_hsotg_udc_start(struct usb_gadget *gadget,
>>   	spin_lock_irqsave(&hsotg->lock, flags);
>>   	s3c_hsotg_init(hsotg);
>>   	s3c_hsotg_core_init_disconnected(hsotg);
>> +	hsotg->enabled = 1;
>> +	hsotg->connected = 0;
>>   	spin_unlock_irqrestore(&hsotg->lock, flags);
>>
>>   	dev_info(hsotg->dev, "bound driver %s\n", driver->driver.name);
>> @@ -2961,6 +2963,8 @@ static int s3c_hsotg_udc_stop(struct usb_gadget *gadget,
>>
>>   	hsotg->driver = NULL;
>>   	hsotg->gadget.speed = USB_SPEED_UNKNOWN;
>> +	hsotg->enabled = 0;
>> +	hsotg->connected = 0;
>>
>>   	spin_unlock_irqrestore(&hsotg->lock, flags);
>>
>> @@ -2999,11 +3003,14 @@ static int s3c_hsotg_pullup(struct usb_gadget *gadget, int is_on)
>>   	dev_dbg(hsotg->dev, "%s: is_on: %d\n", __func__, is_on);
>>
>>   	spin_lock_irqsave(&hsotg->lock, flags);
>> +
>>   	if (is_on) {
>>   		clk_enable(hsotg->clk);
>> +		hsotg->connected = 1;
>>   		s3c_hsotg_core_connect(hsotg);
>>   	} else {
>>   		s3c_hsotg_core_disconnect(hsotg);
>> +		hsotg->connected = 0;
>>   		clk_disable(hsotg->clk);
>>   	}
>>
>> @@ -3652,16 +3659,18 @@ static int s3c_hsotg_suspend(struct platform_device *pdev, pm_message_t state)
>>   		dev_info(hsotg->dev, "suspending usb gadget %s\n",
>>   			 hsotg->driver->driver.name);
>>
>> -	spin_lock_irqsave(&hsotg->lock, flags);
>> -	s3c_hsotg_core_disconnect(hsotg);
>> -	s3c_hsotg_disconnect(hsotg);
>> -	hsotg->gadget.speed = USB_SPEED_UNKNOWN;
>> -	spin_unlock_irqrestore(&hsotg->lock, flags);
>> +	if (hsotg->enabled) {
> Hmm. Are you sure it's safe to check ->enabled outside of the spinlock?
> What happens if s3c_hsotg_udc_stop() runs right after this, before the
> spinlock is taken, and disables stuff? Sure, it's a tiny window, but
> still...

This code is called only in system suspend path, when userspace has been 
already frozen.
udc_stop() can be called only as a result of userspace action, so it is 
imho safe to
assume that the above code doesn't need additional locking.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland