From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753039AbcGLBZc (ORCPT ); Mon, 11 Jul 2016 21:25:32 -0400 Received: from mail-io0-f182.google.com ([209.85.223.182]:34735 "EHLO mail-io0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751698AbcGLBZa (ORCPT ); Mon, 11 Jul 2016 21:25:30 -0400 MIME-Version: 1.0 In-Reply-To: <20160711093918.GE5823@ulmo.ba.sec> References: <20160615021204.GA11507@kroah.com> <20160615143720.GA23483@ulmo.ba.sec> <20160711093918.GE5823@ulmo.ba.sec> From: David Hsu Date: Mon, 11 Jul 2016 18:25:26 -0700 Message-ID: Subject: Re: [PATCH] pwm: Create device class for pwm channels To: Thierry Reding Cc: Greg KH , linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.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 On Mon, Jul 11, 2016 at 2:39 AM, Thierry Reding wrote: > On Wed, Jun 15, 2016 at 04:52:56PM -0700, David Hsu wrote: >> On Wed, Jun 15, 2016 at 7:37 AM, Thierry Reding >> wrote: >> > On Tue, Jun 14, 2016 at 07:12:04PM -0700, Greg KH wrote: >> >> From: David Hsu >> >> >> >> Pwm channels don't send uevents when exported, this change adds the >> >> channels to a pwm class and set their device type to pwm_channel so >> >> uevents are sent. >> >> >> >> To do this properly, the device names need to change to uniquely >> >> identify a channel. This change is from pwmN to pwm-(chip->base):N >> >> >> >> Signed-off-by: David Hsu >> >> Signed-off-by: Greg Kroah-Hartman >> >> --- >> >> Documentation/pwm.txt | 6 ++++-- >> >> drivers/pwm/sysfs.c | 15 ++++++++++++--- >> >> 2 files changed, 16 insertions(+), 5 deletions(-) >> >> >> >> Note, this patch came from David with his work on a system that has >> >> dynamic PWM devices and channels, and we needed some way to tell >> >> userspace what is going on when they are added or removed. If anyone >> >> knows any other way of doing this that does not involve changing the pwm >> >> names, please let us know. >> > >> > Is it truly PWM channels that dynamically appear and disappear? I'd be >> > interested in how that's achieved, because there are probably other >> > issues that will manifest if you do that. Do you have a pointer to the >> > work that David's been undertaking? Generally some more context on the >> > use-case would be helpful here. >> >> Only PWM devices are dynamic, the number of channels exposed by >> devices do not change after they've been added to the system. > > In that case, would it not be enough to use the uevents generated by the > addition and removal of the PWM chip devices to/from sysfs? We need channel level granularity to modify permissions for sysfs nodes that are created when the channels are exported. > >> > Also I'd prefer if this avoided using chip->base here, because it exists >> > purely for legacy purposes and is supposed to go away eventually. >> > >> > Thierry >> >> Would using dev_name(parent) be an acceptable alternative? > > Yes, that sounds like a more sensible choice to me. Thanks Thierry, I'll send out a v2 shortly. It also occurred to me that this change could affect apps that have the previous name hard coded. I can create a link pointing to the new name but wanted to see if there's a better recommendation or if it's required. David > > Thierry