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From: Kukjin Kim <kgene.kim@samsung.com>
To: "'Lars-Peter Clausen'" <lars@metafoo.de>
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, 07 Mar 2011 15:42:56 +0900	[thread overview]
Message-ID: <031101cbdc92$e6c44730$b44cd590$%kim@samsung.com> (raw)
In-Reply-To: <4D6B7FE6.8090802@metafoo.de>

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@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

Hi Lars,

Ok, will apply :)
Thanks.

Best regards,
Kgene.
--
Kukjin Kim <kgene.kim@samsung.com>, Senior Engineer,
SW Solution Development Team, Samsung Electronics Co., Ltd.


  reply	other threads:[~2011-03-07  7:14 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
2011-03-07  6:42           ` Kukjin Kim [this message]
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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