Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933474Ab3GPQEL (ORCPT ); Tue, 16 Jul 2013 12:04:11 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:54387 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933260Ab3GPQEJ (ORCPT ); Tue, 16 Jul 2013 12:04:09 -0400 Message-ID: <51E56EF3.5040506@wwwdotorg.org> Date: Tue, 16 Jul 2013 10:04:03 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Christian Ruppert CC: Linus Walleij , Patrice CHOTARD , "linux-kernel@vger.kernel.org" , Grant Likely , Rob Herring , Rob Landley , Sascha Leuenberger , Pierrick Hascoet , devicetree-discuss@lists.ozlabs.org, linux-doc@vger.kernel.org, Alexandre Courbot Subject: Re: [PATCH 2/4] pinmux: Add TB10x pinmux driver References: <20130618092516.GC18663@ab42.lan> <1371547751-13873-2-git-send-email-christian.ruppert@abilis.com> <51C23222.2060906@wwwdotorg.org> <20130626115051.GC7095@ab42.lan> <51CB279A.1090404@wwwdotorg.org> <20130705094859.GA27196@ab42.lan> <51D71337.6030409@wwwdotorg.org> <20130708130222.GA6402@ab42.lan> <51DDB5B8.5060909@wwwdotorg.org> <20130716084755.GB10914@ab42.lan> In-Reply-To: <20130716084755.GB10914@ab42.lan> X-Enigmail-Version: 1.4.6 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: 4188 Lines: 96 On 07/16/2013 02:47 AM, Christian Ruppert wrote: > On Wed, Jul 10, 2013 at 01:27:52PM -0600, Stephen Warren wrote: >> On 07/08/2013 07:02 AM, Christian Ruppert wrote: >> ... >>> OK, a small drawing of our hardware should make this clear, let's take >>> an imaginary example of one port with 10 pins, one i2c interface, one >>> spi interface and one GPIO bank: >>> >>> | mux N-1| >>> +........+ >>> | | 2 >>> | +--/-- i2c >>> | | >>> 10 | | 4 >>> Pins --/--+ mux N +--/-- spi >>> | | >>> | | 10 >>> | +--/-- GPIO >>> | | >>> +........+ >>> | mux N+1| >>> >>> This example shows the mux N inside the pin controller. It controls >>> all pins associated to port N through a single register value M. Let's >>> assume the pins are configured as follows in function of the register >>> value: >>> >>> pin M=0 M=1 M=2 M=3 >>> 0 GPIO0 SPI_MISO GPIO0 SPI_MISO >>> 1 GPIO1 SPI_MOSI GPIO1 SPI_MOSI >>> 2 GPIO2 SPI_CK GPIO2 SPI_CK >>> 3 GPIO3 SPI_CS GPIO3 SPI_CS >>> 4 GPIO4 GPIO4 GPIO4 GPIO4 >>> 5 GPIO5 GPIO5 GPIO5 GPIO5 >>> 6 GPIO6 GPIO6 GPIO6 GPIO6 >>> 7 GPIO7 GPIO7 GPIO7 GPIO7 >>> 8 GPIO8 GPIO8 I2C_SDA I2C_SDA >>> 9 GPIO9 GPIO9 I2C_SCL I2C_SCL >> >> >> In that scenario, in the language of Linux's pinctrl subsystem, what you >> have is: >> >> 10 pins, named 0..9 >> 1 pin group, named perhaps "mux N". >> 4 different functions; values M==0, 1, 2, 3. >> >>> We now have three pin groups defined, corresponding to the chip-side >>> ports of the pin controller: >>> GPIO = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} >>> SPI = {0, 1, 2, 3} >>> I2C = {8, 9} >> >> You would usually only define pin groups for the pin/ball/package side >> of the pinmux HW. IIRC, you're also wanting to define pin groups for the >> intra-chip side of the pinmux HW. However, you're not muxing functions >> onto those pingroups; they're just there to help with naming the >> GPIO<->pinmux mapping. You only mux functions onto the pin/ball/package >> side pins/pingroups. > > Well, the GPIO<->pinmux mapping is not the only reason for defining > these groups wrt. the chip-side of the pin controller. The other reasons > are: > - Make different interfaces on the same MUX orthogonal wrt. each > other, i.e. make it possible to request one independently of the > other. In the example above, SPI and I2C can be requested completely > independently and the pin controller driver decides which mode to > use. But the pinctrl subsystem and bindings don't have any concept of that; what gets requested is the pins on the chip, or the "outer" side of the pin controller. There's no concept of resource management for the "inside" of the pin controller. > - Make pin allocation more fine-grained (in the example above, only > pins 0-4 are "allocated" in case SPI is requested). This makes > GPIO<->interface pin conflict management more natural. I think you'd want to either: a) Just deal with this in the driver; it knows the HW, and it knows which mux function is selected for each mux, and hence knows exactly which pins can be requested as GPIOs for each combination, and can therefore allow/disallow any GPIO request or mux function change. b) Extend the pinctrl core to know about this explicitly, and pass information to the pinctrl core. Presumably, for each combination of (pingroup, mux function), you'd need a list or bitmask indicating which pins within the pingroup are actually used. Then, the pinctrl core can perform all the validation. If you do this, you don't need to invent new pinctrl groups in order to try and shoe-horn this into pinctrl. -- 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/