linux-kernel - Re: [PATCHv6 6/8] usb: dwc2: gadget: Do not fail probe if there isn't a clock node

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Message-ID: <5453E393.3090505@opensource.altera.com>
Date:	Fri, 31 Oct 2014 14:31:31 -0500
From:	Dinh Nguyen <dinguyen@...nsource.altera.com>
To:	<balbi@...com>
CC:	<paulz@...opsys.com>, <dinh.linux@...il.com>,
	<swarren@...dotorg.org>, <b.zolnierkie@...sung.com>,
	<matthijs@...in.nl>, <r.baldyga@...sung.com>,
	<jg1.han@...sung.com>, <sachin.kamat@...aro.org>,
	<ben-linux@...ff.org>, <dianders@...omium.org>,
	<kever.yang@...k-chips.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv6 6/8] usb: dwc2: gadget: Do not fail probe if there isn't
 a clock node

On 10/31/2014 12:42 PM, Felipe Balbi wrote:
> Hi,
> 
> On Fri, Oct 31, 2014 at 10:20:06AM -0500, Dinh Nguyen wrote:
>>>> @@ -339,7 +339,8 @@ static void dwc2_handle_wakeup_detected_intr(struct dwc2_hsotg *hsotg)
>>>>  		}
>>>>  		/* Change to L0 state */
>>>>  		hsotg->lx_state = DWC2_L0;
>>>> -		call_gadget(hsotg, resume);
>>>> +		if (!IS_ERR(hsotg->clk))
>>>> +			call_gadget(hsotg, resume);
>>>
>>> instead of exposing the clock detail to the entire driver, add IS_ERR()
>>> checks to resume and suspend instead. In fact, NULL is a valid clock, so
>>> you might as well:
>>>
>>> 	clk = clk_get(foo, bar);
>>> 	if (IS_ERR(clk))
>>> 		dwc->clk = NULL;
>>> 	else
>>> 		dwc->clk = clk;
>>>
>>> Then you don't need any IS_ERR() checks sprinkled around the driver.
>>
>> But we would still need to check for the clock before accessing gadget
>> functionality right?
>>
>> 	if (dwc2->clk)
>> 		call_gadget();
> 
> Read my comment again. "NULL is a valid clock".  Look at what
> clk_enable() does when a NULL pointer is passed:
> 
> static int __clk_enable(struct clk *clk)
> {
> 	int ret = 0;
> 
> 	if (!clk)
> 		return 0;
> 
> 	if (WARN_ON(clk->prepare_count == 0))
> 		return -ESHUTDOWN;
> 
> 	if (clk->enable_count == 0) {
> 		ret = __clk_enable(clk->parent);
> 
> 		if (ret)
> 			return ret;
> 
> 		if (clk->ops->enable) {
> 			ret = clk->ops->enable(clk->hw);
> 			if (ret) {
> 				__clk_disable(clk->parent);
> 				return ret;
> 			}
> 		}
> 	}
> 
> 	clk->enable_count++;
> 	return 0;
> }
> 
> int clk_enable(struct clk *clk)
> {
> 	unsigned long flags;
> 	int ret;
> 
> 	flags = clk_enable_lock();
> 	ret = __clk_enable(clk);
> 	clk_enable_unlock(flags);
> 
> 	return ret;
> }
> EXPORT_SYMBOL_GPL(clk_enable);

Ah yes, thanks for the explanation. So if clk=NULL, it just return 0.
But what I'm saying is that if the driver is configured for dual-role
mode, and no clock is specified, then the driver should not be accessing
any gadget functionality.

So as the patch series stands right now, if I swap out an A connector to
a B-connector, then I get a connect_id_status change interrupt. The
status would show a device and I would initialize the gadget portion of
the driver.

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
index 44c609f..96810f7 100644
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -1371,7 +1371,8 @@ static void dwc2_conn_id_status_change(struct
work_struct *work)
                hsotg->op_state = OTG_STATE_B_PERIPHERAL;
                dwc2_core_init(hsotg, false, -1);
                dwc2_enable_global_interrupts(hsotg);
-               s3c_hsotg_core_init(hsotg);
+               if (hsotg->clk)
+                       s3c_hsotg_core_init(hsotg);

So if I don't have a valid clock, I'll be accessing the peripheral
portion of the IP.

But I guess not having the check for the valid clock here should be fine
as I don't see a case where there can be 2 different clocks for host and
peripheral?


> 
>>>> @@ -400,7 +401,8 @@ static void dwc2_handle_usb_suspend_intr(struct dwc2_hsotg *hsotg)
>>>>  			"DSTS.Suspend Status=%d HWCFG4.Power Optimize=%d\n",
>>>>  			!!(dsts & DSTS_SUSPSTS),
>>>>  			hsotg->hw_params.power_optimized);
>>>> -		call_gadget(hsotg, suspend);
>>>> +		if (!IS_ERR(hsotg->clk))
>>>> +			call_gadget(hsotg, suspend);
>>>>  	} else {
>>>>  		if (hsotg->op_state == OTG_STATE_A_PERIPHERAL) {
>>>>  			dev_dbg(hsotg->dev, "a_peripheral->a_host\n");
>>>> @@ -477,7 +479,8 @@ irqreturn_t dwc2_handle_common_intr(int irq, void *dev)
>>>>  	spin_lock(&hsotg->lock);
>>>>  
>>>>  	if (dwc2_is_device_mode(hsotg))
>>>> -		retval = s3c_hsotg_irq(irq, dev);
>>>> +		if (!IS_ERR(hsotg->clk))
>>>> +			retval = s3c_hsotg_irq(irq, dev);
>>>
>>> wait a minute, if there is no clock we don't call the gadget interrupt
>>> handler ? Why ? Who will disable the IRQ line ?
>>
>> This portion is no static int __clk_enable(struct clk *clk)
> 
> huh ? What I mean is that this has the potential of leaving that IRQ
> line enabled. Imagine you don't have a clock and s3c_hsotg_irq() isn't
> called, then a peripheral IRQ fires, since the handler isn't called, who
> will clear the interrupt ?
> 

Yes, right. This portion of the code is no longer needed when I switched
to use a shared IRQ.

Dinh
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