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RE: [PATCH 1/7] pwm: Add pwm core driver

To: "Arun MURTHY" <arun.murthy@stericsson.com>, linux-omap@vger.kernel.org
Subject: RE: [PATCH 1/7] pwm: Add pwm core driver
From: "Hemanth V" <hemanthv@ti.com>
Date: Tue, 28 Sep 2010 15:04:43 +0530 (IST)
Cc: "Vasily Khoruzhick" <anarsoul@gmail.com>, "eric.y.miao@gmail.com" <eric.y.miao@gmail.com>, "linux@arm.linux.org.uk" <linux@arm.linux.org.uk>, "grinberg@compulab.co.il" <grinberg@compulab.co.il>, "mike@compulab.co.il" <mike@compulab.co.il>, "robert.jarzmik@free.fr" <robert.jarzmik@free.fr>, "marek.vasut@gmail.com" <marek.vasut@gmail.com>, "drwyrm@gmail.com" <drwyrm@gmail.com>, "stefan@openezx.org" <stefan@openezx.org>, "laforge@openezx.org" <laforge@openezx.org>, "ospite@studenti.unina.it" <ospite@studenti.unina.it>, "philipp.zabel@gmail.com" <philipp.zabel@gmail.com>, "mad_soft@inbox.ru" <mad_soft@inbox.ru>, "maz@misterjones.org" <maz@misterjones.org>, "daniel@caiaq.de" <daniel@caiaq.de>, "haojian.zhuang@marvell.com" <haojian.zhuang@marvell.com>, "timur@freescale.com" <timur@freescale.com>, "ben-linux@fluff.org" <ben-linux@fluff.org>, "support@simtec.co.uk" <support@simtec.co.uk>, "arnaud.patard@rtp-net.org" <arnaud.patard@rtp-net.org>, "dgreenday@gmail.com" <dgreenday@gmail.com>, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "mcuelenaere@gmail.com" <mcuelenaere@gmail.com>, "kernel@pengutronix.de" <kernel@pengutronix.de>, "andre.goddard@gmail.com" <andre.goddard@gmail.com>, "jkosina@suse.cz" <jkosina@suse.cz>, "tj@kernel.org" <tj@kernel.org>, "hsweeten@visionengravers.com" <hsweeten@visionengravers.com>, "u.kleine-koenig@pengutronix.de" <u.kleine-koenig@pengutronix.de>, "kgene.kim@samsung.com" <kgene.kim@samsung.com>, "ralf@linux-mips.org" <ralf@linux-mips.org>, "lars@metafoo.de" <lars@metafoo.de>, "dilinger@collabora.co.uk" <dilinger@collabora.co.uk>, "mroth@nessie.de" <mroth@nessie.de>, "randy.dunlap@oracle.com" <randy.dunlap@oracle.com>, "lethal@linux-sh.org" <lethal@linux-sh.org>, "rusty@rustcorp.com.au" <rusty@rustcorp.com.au>, "damm@opensource.se" <damm@opensource.se>, "mst@redhat.com" <mst@redhat.com>, "rpurdie@rpsys.net" <rpurdie@rpsys.net>, "sguinot@lacie.co" <sguinot@lacie.co>, "sameo@linux.intel.com" <sameo@linux.intel.com>, "broonie@opensource.wolfsonmicro.com" <broonie@opensource.wolfsonmicro.com>, "balajitk@ti.com" <balajitk@ti.com>, "rnayak@ti.com" <rnayak@ti.com>, "santosh.shilimkar@ti.com" <santosh.shilimkar@ti.com>, "michael.hennerich@analog.com" <michael.hennerich@analog.com>, "vapier@gentoo.org" <vapier@gentoo.org>, "khali@linux-fr.org" <khali@linux-fr.org>, "jic23@cam.ac.uk" <jic23@cam.ac.uk>, "re.emese@gmail.com" <re.emese@gmail.com>, "linux@simtec.co.uk" <linux@simtec.co.uk>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>, "Linus WALLEIJ" <linus.walleij@stericsson.com>, "Mattias WALLIN" <mattias.wallin@stericsson.com>
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In-reply-to: <F45880696056844FA6A73F415B568C69532DC2FB21@EXDCVYMBSTM006.EQ1STM.loca l>
References: <1285659648-21409-1-git-send-email-arun.murthy@stericsson.com> <1285659648-21409-2-git-send-email-arun.murthy@stericsson.com> <201009281114.31223.anarsoul@gmail.com> <F45880696056844FA6A73F415B568C69532DC2FA8F@EXDCVYMBSTM006.EQ1STM.local> <63731.10.24.255.18.1285663815.squirrel@dbdmail.itg.ti.com> <F45880696056844FA6A73F415B568C69532DC2FB21@EXDCVYMBSTM006.EQ1STM.local>
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>> >> On 28 of September 2010 10:40:42 Arun Murthy wrote:
>> >> > The existing pwm based led and backlight driver makes use of the
>> >> > pwm(include/linux/pwm.h). So all the board specific pwm drivers
>> will
>> >> > be exposing the same set of function name as in
>> include/linux/pwm.h.
>> >> > As a result build fails.
>> >>
>> >> Which build fails? One with multi-SoC support? Please be more
>> specific.
>> > Sure will add this in v2.
>> >
>>
>> Could you clarify for the benefit of all, which specific issues you are
>> trying to address with this patch series
> 1. Now since all the pwm driver export same set of function(pwm_enable, 
> pwm_disable,..), if it happens that there are two pwm driver enabled this
> leads to re-declaration and results in build failure. The proper way to 
> handle this would be to have a pwm core function, and let all the pwm
> drivers register to the pwm core driver.
> 2. The above scenario also occurs in place of multi-soc environment. Lets say 
> OMAP has a pwm module and that is being used for primary lcd backlight
> and twl has a backlight that is being used for controlling the charging led 
> brightness. In this case there exists 2 pwm drivers and one pwm driver
> will be used by pwm_bl.c and other by leds-pwm.c

Speaking specifically of OMAP4, twl6030 supports multiple PWMs i.e for 
display/keypad backlight, charging
led. But there should not be need for multiple drivers since twl6030-pwm should 
be able to support
all these (currently it doesnot though). So there would single pwm_enable, 
pwm_disable exported and driver
internally takes care configuring the correct PWM based on id. Would it not be 
similar
situation for other hardware also.

Thanks
Hemanth



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