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: <5453E97F.7000305@opensource.altera.com>
Date:	Fri, 31 Oct 2014 14:56:47 -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 02:31 PM, Dinh Nguyen wrote:
> 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?
> 

Ah...nevermind. I don't need to check for clocks at all because in
dwc2_gadget_init(), the clock node check comes before
usb_add_gadget_udc(). Thus without a clock node, gadget functionality is
disabled already.

Thanks,
Dinh

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