linux-kernel - Re: [PATCH 08/09] ARM: s3c2440: gta02: Request usb pullup pin before using it

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Message-ID: <4D748292.7030302@metafoo.de>
Date:	Mon, 07 Mar 2011 08:00:34 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Kukjin Kim <kgene.kim@...sung.com>
CC:	'Ben Dooks' <ben-linux@...ff.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/09] ARM: s3c2440: gta02: Request usb pullup pin before
 using it

On 03/07/2011 07:42 AM, Kukjin Kim wrote:
> Lars-Peter Clausen wrote:
>>
>> On 02/28/2011 11:44 AM, Kukjin Kim wrote:
>>> Lars-Peter Clausen wrote:
>>>>
>>>> On 02/28/2011 07:16 AM, Kukjin Kim wrote:
>>>>> Lars-Peter Clausen wrote:
>>>>>>
>>>>>> Request the gpio pin used to control the usb pullup before using it
> to
>>>>> avoid
>>>>>> a
>>>>>> runtime warning about an auto-requested gpio.
>>>>>>
>>>>>> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
>>>>>> ---
>>>>>>  arch/arm/mach-s3c2440/mach-gta02.c |   17 +++++++++++++++--
>>>>>>  1 files changed, 15 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/arm/mach-s3c2440/mach-gta02.c
>>>>> b/arch/arm/mach-s3c2440/mach-
>>>>>> gta02.c
>>>>>> index 1396639..94456fa 100644
>>>>>> --- a/arch/arm/mach-s3c2440/mach-gta02.c
>>>>>> +++ b/arch/arm/mach-s3c2440/mach-gta02.c
>>>>>> @@ -451,11 +451,11 @@ static void gta02_udc_command(enum
>>> s3c2410_udc_cmd_e
>>>>>> cmd)
>>>>>>  	switch (cmd) {
>>>>>>  	case S3C2410_UDC_P_ENABLE:
>>>>>>  		pr_debug("%s S3C2410_UDC_P_ENABLE\n", __func__);
>>>>>> -		gpio_direction_output(GTA02_GPIO_USB_PULLUP, 1);
>>>>>> +		gpio_set_value(GTA02_GPIO_USB_PULLUP, 1);
>>>>>
>>>>> How about following instead?
>>>>> 	gpio_request(GTA02_GPIO_USB_PULLUP, "USB_PULLUP");
>>>>> 	gpio_direction_output(GTA02_GPIO_USB_PULLUP, 1);
>>>>> 	gpio_free(GTA02_GPIO_USB_PULLUP);
>>>>>
>>>>
>>>> I don't think that is a good idea. This gpio should really be reserved
> for
>>>> the
>>>> udc driver. If it is freed again, it could be requested from someone
> else
>>>> which
>>>> could lead to undefined behaviour.
>>>>
>>> Yes right, but I mean the board designer already knows the usage of
>>> regarding GPIOs on his board.
>>> So why do we really need gpio_request for it?...
>>
>> Well, for one because it's part of the gpio-api. You should not call any
>> other
>> gpio functions on a pin unless you've successfully requested that pin.
>> On the other hand this helps debugging and ensures that the same gpio is
> not
>> used by two drivers accident. For example it is also possible to request
>> gpios
>> from userspace using the gpio sysfs. So by keeping the gpio requested it
> wont
>> be possible to request it from userspace by accident. And the gpio will
> also
>> be
>> listed in the gpio debugfs file, which can be helpful for debugging as
> well.
>>
>> - Lars
> 
> Hi Lars,
> 
> Ok, will apply :)
> Thanks.
> 
> Best regards,
> Kgene.
> --
> Kukjin Kim <kgene.kim@...sung.com>, Senior Engineer,
> SW Solution Development Team, Samsung Electronics Co., Ltd.
> 

Hi Kgene

Actually I've prepared another patch, which I'm was about to send in a few
minutes, which moves the controlling of the pullup pin to the udc driver.

- Lars
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