Date:	Fri, 30 Aug 2013 16:14:09 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	George Cherian <george.cherian@...com>
Cc:	balbi@...com, myungjoo.ham@...sung.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	grant.likely@...aro.org, rob@...dley.net, ian.campbell@...rix.com,
	swarren@...dotorg.org, mark.rutland@....com, pawel.moll@....com,
	rob.herring@...xeda.com, linux-omap@...r.kernel.org,
	linux-usb@...r.kernel.org, bcousson@...libre.com,
	davidb@...eaurora.org, arnd@...db.de, swarren@...dia.com,
	popcornmix@...il.com
Subject: Re: [PATCH v3 1/3] extcon: extcon-gpio-usbvid: Generic USB VBUS/ID
 detection via GPIO

Hi George,

In addition, I add answer about that device driver control gpio pin directly.

On 08/30/2013 03:15 PM, George Cherian wrote:
> Hi Chanwoo,
> 
> On 8/30/2013 5:41 AM, Chanwoo Choi wrote:
>> Hi George,
>>
>> On 08/29/2013 10:45 PM, George Cherian wrote:
>>> Hi Chanwoo,
>>>
>>>
>>> On 8/29/2013 5:42 PM, Chanwoo Choi wrote:
>>> [big snip ]
>>>>>> I tested various development board based on Samsung Exynos series SoC.
>>>>>> Although some gpio of Exynos series SoC set high state(non zero, 1) as default value,
>>>>>> this gpio state could mean off state, disconnected or un-powered state according to gpio.
>>>>>> Of course, above explanation about specific gpio don't include all gpios.
>>>>>> This is meaning that there is possibility.
>>>>> okay then how about adding a flag for inverted logic too.  something like this
>>>>>
>>>>> if(of_property_read_bool(np,"inverted_gpio))
>>>>>       gpio_usbvid->gpio_inv = 1;
>>>>> And always check on this before deciding?
>>> Is this fine ?
>> OK.
>> But, as Stephen commented on other mail, you should use proper DT helper function.
> okay
>>>>>>>> Second,
>>>>>>>> gpio_usbvid_set_initial_state() dertermine both "USB-HOST" and "USB" cable state at same time
>>>>>>>> in 'case ID_DETCT' according to 'gpio_usbvid->id_gpio'. But, I think that other extcon devices
>>>>>>>> would not control both "USB-HOST" and "USB" cable state at same time.
>>>>>>>>
>>>>>>>> Other extcon devices would support either "USB-HOST" or "USB" cable.
>>>>>>> The driver has 2 configurations.
>>>>>>> 1) supports implementations with both VBUS and ID pin are routed via gpio's for swicthing roles(compatible  gpio-usb-vid).
>>>>>> As you explained about case 1, it is only used on dra7x SoC.
>>>>> No gpio-usb-id is used in dra7xx. dra7xx has got only ID pin routed via gpio.
>>>>>> Other SoC could not wish to control both "USB-HOST" and "USB" cable at same time.
>>> I could'nt actually parse this. You meant since the id_irq_handler handles both USB and USB-HOST cable
>>> its not proper?
>> It's not proper in general case. The generic driver must guarantee all of extcon device using gpio.
>> As far as I know, the generic driver cannot direclty control gpio pin and get value from gpio pin.
>> Almost device driver including in kernel/drivers control gpio pin on specific device driver
>> instead of generic driver.
> But without reading the gpio value how can we set the cable states?

hmm. I mentioned above my answer as following:
	>> As far as I know, the generic driver cannot direclty control gpio pin and get value from gpio pin.
	>> Almost device driver including in kernel/drivers control gpio pin on specific device driver
Because your extcon driver directly control gpio pin so I think your extcon driver isn't generic.

for this driver the assumption is the dedicated gpio
> is always DIR_IN and in the driver we just read the value.

What is DIR_IN?

>>>> I need your answer about above my opinion for other SoC.
>>> So how about this, I have removed the dra7x specific stuffs (gpio-usb-id)
>>>
>>> static void gpio_usbvid_set_initial_state(struct gpio_usbvid *gpio_usbvid)
>>> {
>>>          int id_current, vbus_current;
>>>
>>>      id_current = gpio_get_value_cansleep(gpio_usbvid->id_gpio);
>>>      if (!!id_current == ID_FLOAT)
>>>          extcon_set_cable_state(&gpio_usbvid->edev, "USB-HOST", false);
>>>      else
>>>          extcon_set_cable_state(&gpio_usbvid->edev, "USB-HOST", true);
>>>
>>>      vbus_current = gpio_get_value_cansleep(gpio_usbvid->vbus_gpio);
>>>       if (!!vbus_current == VBUS_ON)
>>>          extcon_set_cable_state(&gpio_usbvid->edev, "USB", true);
>>>      else
>>>          extcon_set_cable_state(&gpio_usbvid->edev, "USB", false);
>>> }
>>>
>>> and the irq handlers like this
>>>
>>> static irqreturn_t id_irq_handler(int irq, void *data)
>>> {
>>>          struct gpio_usbvid *gpio_usbvid = (struct gpio_usbvid *)data;
>>>          int id_current;
>>>
>>>          id_current = gpio_get_value_cansleep(gpio_usbvid->id_gpio);
>>>          if (id_current == ID_GND)
>>>                  extcon_set_cable_state(&gpio_usbvid->edev, "USB-HOST", true);
>>>          else
>>>                  extcon_set_cable_state(&gpio_usbvid->edev, "USB-HOST", false);
>>>          return IRQ_HANDLED;
>>> }
>>>
>>> static irqreturn_t vbus_irq_handler(int irq, void *data)
>>> {
>>>          struct gpio_usbvid *gpio_usbvid = (struct gpio_usbvid *)data;
>>>          int vbus_current;
>>>
>>>          vbus_current = gpio_get_value_cansleep(gpio_usbvid->vbus_gpio);
>>>          if (vbus_current == VBUS_OFF)
>>>                  extcon_set_cable_state(&gpio_usbvid->edev, "USB", false);
>>>          else
>>>                  extcon_set_cable_state(&gpio_usbvid->edev, "USB", true);
>>>
>>>          return IRQ_HANDLED;
>>> }
>> I know your intention dividing interrupt handler for each cable.
>> But I don't think this driver must guarantee all of extcon device using gpio.
>>
>> For example,
>> below three SoC wish to detect USB/USB-HOST cable with each different methods.
>>
>> "SoC A" wish to detect USB/USB-HOST cable through only one gpio pin.
> 
> You mean to say that both USB ID pin and VBUS are connected to same gpio?
> If so that is a really bad h/w design and it will not fly.
> Or, you meant that only USB ID pin is connected to single gpio and it controls the state of the USB/USB-HOST cables?
> If so thats what exactly the v3 driver did with compatible gpio-usb-id.
> 
>> "SoC B" wish to detect USB/USB-HOST cable through ADC value instead of gpio pin.
> 
> Via ADC this driver should never be used , it should be extcon-adc-usbvid driver and not extcon-gpio-usbvid driver.
>> "SoC C" wish to detect USB/USB-HOST cable through two gpio pin because USB connected on gpio an USB-HOST connected on another.
> 
> Whatever modifications above should meet this need  in combination with named gpios (id_gpio and vbus_gpio in dt)as stephen pointed.
> But still i feel the above modification would even support Soc A provided the code registered for the notifier could handle it properly.
>>
>> In addition,
>> if "SoC A/C" wish to write some data to own specific registers for proper opeating,
>> Could we write some data to register on generic driver?
> 
> Yes definitely, those register configuration should not be part of this driver and it should be done in the notifier handler.
>>
>> Finally,
>> "SoC D" wish to detect USB/USB-HOST/JIG cable through two gpio pin
> Correct me If I am wrong, USB JIG is not a standard cable. so for supporting that anyways you need to have
> a different driver.
>> - one gpio may detect either USB or USB-HOST and another may detect JIG cable
> I assume u meant the USB ID pin is connected to one gpio and based on it value USB/USB-HOST  is detected.
>> or one gpio may detect either USb or JIG and another may detect USB-HOST cable.
>  As I mentioned earlier these are gpios configured as input and if you try to drive with 2 sources (USB and JIG or USB and USB-HOST etc)
> then its a potentially bad design . If at all we need to identify all 3 then there should be 3 dedicated gpios.
> 
>> That way, there are many cases we cannot guarantee all of extcon devices.
>>
>> I think this driver could support dra7x series SoC but as I mentioned,
>> this driver may not guarantee all of cases.
> I am sorry, I feel it supports all standard cases except for something like a JIG cable which is not standard.
>>
>>> [snip]
>>>>>> I have some confusion. I need additional your explanation.
>>>>>> Could this driver register only one interrupt handler either id_irq_handler() or vbus_irq_handler()?
>>>>> If compatible == ID_DETECT, only one handler --> id_irq_handler() and it will handle both USB and USB-HOST
>>>>>> or
>>>>>> Could this driver register two interrupt handler both id_irq_handler() or vbus_irq_handler()?
>>>>> If compatible == VBUS_ID_DETECT, 2 handlers --> id_irq_handler() will handle USB-HOST and vbus_irq_handler will handle USB.
>>>> As you mentioned, we cannot only control either USB or USB-HOST cable on this extcon driver.
>>>> This extcon driver is only suitable dra7x SoC.
>>> Do you still feel its dra7x specific if i modify it as above?
>> I commented above about your modification.
>>
>>>> Because id_irq_handler() control both "USB-HOST" and "USB" cable at same time,
>>>> you need this setting order between "USB-HOST" and "USB" cable.
>>>>> yes
>>>> I think that the setting order between cables isn't general. It is specific method for dra7x SoC.
>>> So if i remove that part then?
>> The setting order should be removed in generic driver.
> Yes I agree and should be done by the subscriber to the notifier.
>>
>>>>>> Did you think that SoC should always connect either "USB-HOST" cable or "USB" cable?
>>>>> No,  even if a physical cable is not connected it should  default to either USB-HOST or USB
>>>> It isn't general.
>>>>
>>>> If physical cable isn't connected to extcon device, the state both USB-HOST and USB cable
>>>> should certainly be zero. Because The extcon consumer driver could set proper operation
>>>> according to cable state.
>>> okay
>>>>>> I don't know this case except for dra7x SoC. So, I think it has dependency on specific SoC.
>>>> I need your answer about above my opinion.
>>> Hope i could answer you :-)
>>>>>> and can't agree as generic extcon gpio driver.
>> Thanks,
>> Chanwoo Choi
> 
> 

Thanks,
Chanwoo Choi

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