From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pantelis Antoniou Subject: Re: [RFC Patch] gpio: add GPIO hogging mechanism Date: Wed, 29 Oct 2014 18:42:48 +0200 Message-ID: <2BA5D07E-B5EF-49E1-BFD2-310A6C5F3FE4@gmail.com> References: <1413922198-29373-1-git-send-email-bparrot@ti.com> <3D00ADB3-00B3-40A8-8263-444BCADDAC33@gmail.com> <20141029163445.GB29965@ti.com> Mime-Version: 1.0 (Mac OS X Mail 8.0 \(1990.1\)) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20141029163445.GB29965@ti.com> Sender: linux-kernel-owner@vger.kernel.org To: Benoit Parrot Cc: Linus Walleij , linux-gpio@vger.kernel.org, linux-kernel , devicetree@vger.kernel.org List-Id: devicetree@vger.kernel.org Hi Benoit, > On Oct 29, 2014, at 18:34 , Benoit Parrot wrote: >=20 > Pantelis, >=20 > Thanks for the feedback. >=20 > Pantelis Antoniou wrote on Wed [2014-Oc= t-29 10:53:44 +0200]: >> Hi Benoit, >>=20 >>> On Oct 21, 2014, at 23:09 , Benoit Parrot wrote: >>>=20 >>> Based on Boris Brezillion work this is a reworked patch >>> of his initial GPIO hogging mechanism. >>> This patch provides a way to initally configure specific GPIO >>> when the gpio controller is probe. >>>=20 >>> The actual DT scanning to collect the GPIO specific data is perform= ed >>> as part of the gpiochip_add(). >>>=20 >>> The purpose of this is to allows specific GPIOs to be configured >>> without any driver specific code. >>> This particularly usueful because board design are getting >>> increassingly complex and given SoC pins can now have upward >>> of 10 mux values a lot of connections are now dependent on >>> external IO muxes to switch various modes and combination. >>>=20 >>> Specific drivers should not necessarily need to be aware of >>> what accounts to a specific board implementation. This board level >>> "description" should be best kept as part of the dts file. >>>=20 >>=20 >> This look like it=E2=80=99s going to the right direction. I have a f= ew general >> comments at first. >>=20 >> 1) It relies on dubious DT binding of having sub-nodes of the >> gpio device implicitly defining hogs. >=20 > I think in this instance the nodes are explicitly defining hogs. > Please clarify. What would you like to see here? >>=20 Any subnodes are implicitly taken as hog definitions. This is not right= because gpio controllers might have subnodes that they use for another purpose. >> 2) There is no way for having hogs inserted dynamically as far as I = can tell, and >> no way to remove a hog either. >=20 > The original patch was allowing that but, Linus's review comment sugg= ested this feature be=20 > part of the gpio-controller's gpiochip_add() hook only. >=20 If it=E2=80=99s not possible to remove a hog, then it=E2=80=99s no good= for my use case in which the gpios get exported and then removed. >>=20 >> 3) I=E2=80=99m not very fond of having this being part of the gpio c= ontroller. This >> configuration conceptually has little to do with the gpio controller= per se, >> it is more of a board specific thing. Why not come up with a gpio-ho= g driver that >> references GPIOs? That way with a single gpio-hog driver instance yo= u could setup >> all the GPIO-hogging configuration for all GPIOs on the board, even = one that >> lie on different GPIO controllers. >=20 > Again this follows Linus's review comment. > I agree that it prevent a centralize spot where all hog would be defi= ned but it has the advantages of not relying on PROBE_DEFER. > I mean since all "gpio-hogs" would be defined in a single board dts f= ile it would not be that hard to figure out the big picture anyways. >=20 There won=E2=80=99t be a single board dts file if you=E2=80=99re using = things like overlays. >>=20 >>=20 >>> Signed-off-by: Benoit Parrot >>> --- >>> Documentation/devicetree/bindings/gpio/gpio.txt | 33 +++++++++ >>> drivers/gpio/gpiolib-of.c | 99 ++++++++++++++= +++++++++++ >>> drivers/gpio/gpiolib.c | 81 ++++++++++++++= ++++++ >>> include/linux/of_gpio.h | 11 +++ >>> 4 files changed, 224 insertions(+) >>>=20 >>=20 >> Regards >>=20 >> =E2=80=94 Pantelis >>=20 >=20 > Regards, > Benoit Regards =E2=80=94 Pantelis