Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756447AbbFQMhu (ORCPT ); Wed, 17 Jun 2015 08:37:50 -0400 Received: from eusmtp01.atmel.com ([212.144.249.242]:58990 "EHLO eusmtp01.atmel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754902AbbFQMhn (ORCPT ); Wed, 17 Jun 2015 08:37:43 -0400 Date: Wed, 17 Jun 2015 14:38:16 +0200 From: Ludovic Desroches To: Stephen Warren CC: Ludovic Desroches , , , , , , Subject: Re: [RESEND PATCH 1/2] pinctrl: change function behavior for per pin muxing controllers Message-ID: <20150617123816.GB12295@odux.rfo.atmel.com> Mail-Followup-To: Stephen Warren , linux-arm-kernel@lists.infradead.org, linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linus.walleij@linaro.org, nicolas.ferre@atmel.com References: <1433948699-19800-1-git-send-email-ludovic.desroches@atmel.com> <1433948699-19800-2-git-send-email-ludovic.desroches@atmel.com> <557EF60D.8020007@wwwdotorg.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <557EF60D.8020007@wwwdotorg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8531 Lines: 182 Hi Stephen, On Mon, Jun 15, 2015 at 09:58:05AM -0600, Stephen Warren wrote: > On 06/10/2015 09:04 AM, Ludovic Desroches wrote: > >When having a controller which allows per pin muxing, declaring with > >which groups a function can be used is a useless constraint since groups > >are something virtual. > > This isn't true. > > Irrespective of whether a particular piece of pinmux HW can control the mux > function for each pin individually, or only in groups, it's quite likely > that each function can only be selected onto a subset of those pins or > groups. Requiring the pinctrl driver to inform the core which set of > pins/groups particular functions can be selected onto seems quite > reasonable. > > In my opinion at least, for HW that can select the mux function at the > per-pin level, the only sensible set of groups is one group per pin with > each group containing a single pin. Any other use of groups is a > SW/user-level construct, and is something unrelated to why the pinctrl > subsystem supports groups. If we want to represent those groups in pinctrl, > there should be two separate sets of groups; one to represent the actual HW > capabilities, and one to represent the SW/user-level convenience > abstractions. Groups that I would like to use are not something related to the user or software. It's an hardware reality but they would be more flexibles. Usually the muxing is done by selecting a function (which seems to be device related: usart, spi, etc.), then you select on which pins you want this function. In my case, I can't select a function only by choosing a mux. It is a combination of the mux and the pin on which it is applied. So my functions will be GPIO, A, B, C, etc. If I use function A on pin 12, I will have my i2c clock signal but I can have this signal on pin 58 if I use function C. Do you understand what I mean? It's not very easy to explain... So here is a real example: -------------------------------------------------- | | pio peripheral | -------------------------------------------------- | signal | dir | func | signal | dir | ioset | -------------------------------------------------- | PA8 | I/O | A | SDMMC0_DAT6 | I/O | 1 | | | | B | QSPI1_IO1 | I/O | 1 | | | | D | TCLK5 | I | 1 | | | | E | FLEXCOM2_IO2 | I/O | 1 | | | | F | NWE/NANDWE | O | 2 | -------------------------------------------------- | PD28 | I/O | A | SPI1_NPCS0 | I/O | 3 | | | | B | TDI | I/O | 3 | | | | C | FLEXCOM2_IO2 | I | 2 | -------------------------------------------------- You are right that having a group per pin is a solution. If I follow your proposal (tell me if I'm wrong): - I will have 128 groups since I have 128 pins. - I will have functions GPIO, A, B, C, D, E, F. - I have to give the groups which can achieve a function so I will have 128 groups for each function. It means 128 x 7 = 896 groups. Does it seems to be something reasonable and intelligible? From my point of view no. And what about the sysfs readability? With my current implementation, I have something quite understandable for the user if he needs to check the pinmuxing: # cat /sys/kernel/debug/pinctrl/ahb\:apb\:pinctrl@fc038000/pinmux-pins pin 17 (PA17): (MUX UNCLAIMED) (GPIO UNCLAIMED) pin 18 (PA18): b0000000.sdio-host (GPIO UNCLAIMED) function E group sdmmc1_0 pin 19 (PA19): b0000000.sdio-host (GPIO UNCLAIMED) function E group sdmmc1_0 # cat /sys/kernel/debug/pinctrl/pinctrl-maps Pinctrl maps: device b0000000.sdio-host state default type MUX_GROUP (2) controlling device ahb:apb:pinctrl@fc038000 group sdmmc1_0 function E device b0000000.sdio-host state default type CONFIGS_PIN (3) controlling device ahb:apb:pinctrl@fc038000 pin PA28 config 00010003 device b0000000.sdio-host state default type CONFIGS_PIN (3) controlling device ahb:apb:pinctrl@fc038000 pin PA18 config 00010003 Doing as you propose, I assume the result should be: # cat /sys/kernel/debug/pinctrl/ahb\:apb\:pinctrl@fc038000/pinmux-pins pin 17 (PA17): (MUX UNCLAIMED) (GPIO UNCLAIMED) pin 18 (PA18): b0000000.sdio-host (GPIO UNCLAIMED) function E group PA18 pin 19 (PA19): b0000000.sdio-host (GPIO UNCLAIMED) function E group PA19 # cat /sys/kernel/debug/pinctrl/pinctrl-maps Pinctrl maps: device b0000000.sdio-host state default type MUX_GROUP (2) controlling device ahb:apb:pinctrl@fc038000 group PA28 function E device b0000000.sdio-host state default type CONFIGS_PIN (3) controlling device ahb:apb:pinctrl@fc038000 pin PA28 config 00010003 device b0000000.sdio-host state default type MUX_GROUP (2) controlling device ahb:apb:pinctrl@fc038000 group PA18 function E device b0000000.sdio-host state default type CONFIGS_PIN (3) controlling device ahb:apb:pinctrl@fc038000 pin PA18 config 00010003 I think it is more difficult to understand what is done here. I have sent patches months ago trying to improve things by having something more flexible. I don't think I introduce too big changes. The only answers I got were from people thinking that pinctrl framework conception is not good to fit all kind of controllers. I re-sent the patch series to gain more expose and have no answer... I wanted to use as much as possible the generic stuff we have in order to not add a new "custom" implementation. If it is such a big deal to do these changes because you (or other people) think that we can use it as is to describe our pinmux/pinconf configuration then I can switch to a custom implementation too and not use the pinconf generic dt_node_to_map. I think this solution is not encouraged by Linus who prefers to cling the generic infrastructure, isn'it? This is exactly why I took this approach. FYI: some context about these patches: The RFC I send long time ago: http://www.spinics.net/lists/linux-gpio/msg05198.html My second attempt: http://comments.gmane.org/gmane.linux.kernel.gpio/7767 It is not the first time, there are discussions about it. Sascha sent a patch which fits part of my needs: http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/318452.html And it seems some controllers use this approach: http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/318452.html Regards Ludovic -- 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/