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From: Lars-Peter Clausen <lars@metafoo.de>
To: Kukjin Kim <kgene.kim@samsung.com>
Cc: "'Ben Dooks'" <ben-linux@fluff.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/09] ARM: s3c2440: gta02: Request usb pullup pin before using it
Date: Mon, 28 Feb 2011 11:58:46 +0100	[thread overview]
Message-ID: <4D6B7FE6.8090802@metafoo.de> (raw)
In-Reply-To: <003201cbd734$79d87050$6d8950f0$%kim@samsung.com>

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@metafoo.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

  reply	other threads:[~2011-02-28 10:57 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-07  1:51 [PATCH 01/09] ARM: s3c2442: gta02: Fix usage gpio bank j pin definitions Lars-Peter Clausen
2011-02-07  1:51 ` [PATCH 02/09] ARM: s3c2440: gta02: Register PCM device Lars-Peter Clausen
2011-02-28  6:38   ` Kukjin Kim
2011-02-07  1:51 ` [PATCH 03/09] ARM: s3c2440: gta02: Add button support Lars-Peter Clausen
2011-02-28  6:37   ` Kukjin Kim
2011-02-07  1:51 ` [PATCH 04/09] ARM: s3c2440: gta02: Select missing S3C_DEV_USB_HOST Lars-Peter Clausen
2011-02-28  6:31   ` Kukjin Kim
2011-02-07  1:51 ` [PATCH 05/09] ARM: s3c2440: gta02: Fix regulator valid_modes_ops Lars-Peter Clausen
2011-02-28  6:48   ` Kukjin Kim
2011-02-07  1:51 ` [PATCH 06/09] ARM: s3c2440: gta02: Remove state_mem constraints for the pcf50633 regulators Lars-Peter Clausen
2011-02-28  6:26   ` Kukjin Kim
2011-02-28 10:28     ` Lars-Peter Clausen
2011-02-28 10:58       ` Kukjin Kim
2011-02-07  1:51 ` [PATCH 07/09] ARM: s3c2440: gta02: Call regulator_has_full_constraints Lars-Peter Clausen
2011-02-07 11:58   ` Mark Brown
2011-02-08  2:55   ` [PATCH v2 " Lars-Peter Clausen
2011-02-28  6:47     ` Kukjin Kim
2011-02-07  1:52 ` [PATCH 08/09] ARM: s3c2440: gta02: Request usb pullup pin before using it Lars-Peter Clausen
2011-02-28  6:16   ` Kukjin Kim
2011-02-28 10:25     ` Lars-Peter Clausen
2011-02-28 10:44       ` Kukjin Kim
2011-02-28 10:58         ` Lars-Peter Clausen [this message]
2011-03-07  6:42           ` Kukjin Kim
2011-03-07  7:00             ` Lars-Peter Clausen
2011-02-07  1:52 ` [PATCH 09/09] ARM: s3c2440: gta02: Add touchscreen support Lars-Peter Clausen
2011-02-28  6:04   ` Kukjin Kim
2011-02-28 10:44     ` Lars-Peter Clausen
2011-02-28 10:57       ` Kukjin Kim
2011-02-28 11:17   ` [PATCH v2 " Lars-Peter Clausen
2011-02-28 11:56     ` Kukjin Kim
2011-02-18 10:41 ` [PATCH 01/09] ARM: s3c2442: gta02: Fix usage gpio bank j pin definitions Lars-Peter Clausen
2011-02-21  9:58   ` Kukjin Kim
2011-02-28  6:41 ` Kukjin Kim
2011-02-28 10:46   ` Lars-Peter Clausen
2011-02-28 10:49     ` Kukjin Kim

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