linux-kernel - Re: [PATCH] pwm: Create device class for pwm channels

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAH7o3i6o2489ArgLRjhgv6uS+=RFq-dby9zc9vSMfDiQ62o86g@mail.gmail.com>
Date:	Wed, 15 Jun 2016 16:52:56 -0700
From:	David Hsu <davidhsu@...gle.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>, linux-pwm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pwm: Create device class for pwm channels

On Wed, Jun 15, 2016 at 7:37 AM, Thierry Reding
<thierry.reding@...il.com> wrote:
> On Tue, Jun 14, 2016 at 07:12:04PM -0700, Greg KH wrote:
>> From: David Hsu <davidhsu@...gle.com>
>>
>> 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 <davidhsu@...gle.com>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> ---
>>  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.

>
> 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?

Thanks,
David