Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753666Ab1B1K5a (ORCPT ); Mon, 28 Feb 2011 05:57:30 -0500 Received: from mailhost.informatik.uni-hamburg.de ([134.100.9.70]:35466 "EHLO mailhost.informatik.uni-hamburg.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753644Ab1B1K53 (ORCPT ); Mon, 28 Feb 2011 05:57:29 -0500 Message-ID: <4D6B7FE6.8090802@metafoo.de> Date: Mon, 28 Feb 2011 11:58:46 +0100 From: Lars-Peter Clausen User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20101226 Icedove/3.0.11 MIME-Version: 1.0 To: Kukjin Kim CC: "'Ben Dooks'" , 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 References: <1297043521-21903-1-git-send-email-lars@metafoo.de> <1297043521-21903-8-git-send-email-lars@metafoo.de> <000301cbd70f$12367070$36a35150$%kim@samsung.com> <4D6B7826.1030500@metafoo.de> <003201cbd734$79d87050$6d8950f0$%kim@samsung.com> In-Reply-To: <003201cbd734$79d87050$6d8950f0$%kim@samsung.com> X-Enigmail-Version: 1.0.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2387 Lines: 61 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 >>>> --- >>>> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/