Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751870AbdH1Czu (ORCPT ); Sun, 27 Aug 2017 22:55:50 -0400 Received: from mail-ua0-f172.google.com ([209.85.217.172]:34552 "EHLO mail-ua0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751813AbdH1Czp (ORCPT ); Sun, 27 Aug 2017 22:55:45 -0400 X-Google-Smtp-Source: ADKCNb6tZrf+8614yeoYH14sxduYdODmiMlQ3rg6JF6g6u3gJzY1ZzEZJ/g5U64kvtPO0ZOB9gBEjGwqys9fluqDkuM= MIME-Version: 1.0 In-Reply-To: References: <1503418256-5215-1-git-send-email-oleksandrs@mellanox.com> From: Rick Altherr Date: Sun, 27 Aug 2017 19:55:43 -0700 Message-ID: Subject: Re: [patch v6 0/3] JTAG driver introduction To: Linus Walleij Cc: Oleksandr Shamray , "devicetree@vger.kernel.org" , =?UTF-8?B?SmnFmcOtIFDDrXJrbw==?= , Arnd Bergmann , system-sw-low-level@mellanox.com, Greg KH , OpenBMC Maillist , "linux-kernel@vger.kernel.org" , openocd-devel-owner@lists.sourceforge.net, mec@shout.net, Rob Herring , "linux-serial@vger.kernel.org" , vadimp@maellanox.com, Tobias Klauser , "linux-api@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1915 Lines: 46 On Sun, Aug 27, 2017 at 3:30 PM, Linus Walleij wrote: > On Fri, Aug 25, 2017 at 6:52 PM, Rick Altherr wrote: > >>> Incidentally, people are sending patches to expose the FTDI >>> expanders as common GPIO chips under Linux, so we can >>> internally in the kernel or from the usersapce character device >>> access them as "some GPIOs". >> >> I know my team at Google has an internal patch for exactly that. FTDI >> expanders are complicated as they can be used as UART, GPIO, I2C, SPI >> depending on configuration. Our project was using a mix of I2C and >> GPIO so I directly my team to approach it as an MFD. I'd like to see >> all of these use cases handled by the kernel but I understand the >> other viewpoint of relying on libusb for cross-platform compatiblity. > > Hm. I see. But I see people pushing the in-kernel method so I think > it will eventually win out. > SGTM. I'll see if my team can clean up the MFD-based FTDI driver and submit it upstream. >>>>> In my worst nightmare they export GPIO lines using >>>>> the horrid ABI in /sys/gpio/* >>>> >>>> https://sourceforge.net/p/openocd/code/ci/v0.10.0/tree/src/jtag/drivers/sysfsgpio.c >>> >>> Gnah! >>> Whoever writes a slot-in replacement making the character device >>> take precendence wins lots of karma. >> >> If they show up at Linux Plumbers or visit San Jose, I'll take them to >> dinner. I didn't see any docs for the chardev in Documentation. I >> _think_ I understand how it works from reading the relevant sections >> of gpiolib.c but I can see how users end up using sysfs instead. > > I intended tools/gpio/* to be the documentation: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/gpio > > If we need more written documentation we can do it I guess, I haven't been in the habit of looking in tools/. Guess I should be. > > Yours, > Linus Walleij