Message-ID: <20170228140152.GA7073@kroah.com>
Date:   Tue, 28 Feb 2017 15:01:52 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Michał Kępień <kernel@...pniu.pl>
Cc:     Jonathan Woithe <jwoithe@...t42.net>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] fujitsu_init() cleanup

On Tue, Feb 28, 2017 at 02:24:40PM +0100, Michał Kępień wrote:
> > On Tue, Feb 28, 2017 at 09:33:28AM +0100, Micha?? K??pie?? wrote:
> > > GregKH wrote:
> > > > On Mon, Feb 27, 2017 at 10:17:55PM -0800, Darren Hart wrote:
> > > > > GregKH - Can you please confirm the above? Moving an attribute is different than
> > > > > the format and contents, which is what I explicitly documented in
> > > > > Documentation/admin-guide/sysfs-rules.rst (last section).
> > > > 
> > > > Moving an attribute to a different device structure is usually a bad
> > > > idea, if the userspace tool counting on it to be present in a specific
> > > > place breaks.
> > > 
> > > Yes, I am familiar with that premise.  Here is the thing though: I am
> > > unaware of any userspace tool which uses these attributes.  Though,
> > > obviously, that does not mean such tools do not exist.
> > 
> > For what it's worth I too am unaware of any utilities which use the
> > /sys/devices/platform/fujitsu-laptop/ attributes associated with the
> > backlight - this after using the S7020 since 2005.  I would be surprised if
> > any existed since they would have to be specifically for the Fujitsu
> > hardware.  If writing any utility to control the backlight the logical thing
> > to do would be to use the standard backlight attributes in
> > /sys/devices/virtual/backlight/fujitsu-laptop/.
> > 
> > > > But, as you can't be consistent here, don't break userspace please, I'd
> > > > recommend just leaving it alone for now.
> > > 
> > > Darren, in the light of the above I will be awaiting your final call on
> > > this before posting any further patches touching this area.  My number
> > > one priority was to drop the broken backlight-related attributes,
> > > because leaving the other attributes where they currently are does not
> > > prevent achieving a clean split between the two drivers registered by
> > > fujitsu-laptop, which is the ultimate objective of all these cleanups.
> > 
> > As I explained in my response to GregKH earlier and having investigated this
> > in more detail, I have no objection to the removal of the non-standard
> > backlight-related sysfs attributes (brightness_changed, lcd_level and
> > max_brightness).  They are almost certainly unused and their removal will
> > allow a significant cleanup of fujitsu-laptop.  Obviously however there are
> > competing viewpoints which take a bigger picture view so I will defer to
> > Darren's judgement.
> 
> Okay, so it looks like I did the best I could to explain my intentions
> and some confusion crept in anyway, sorry about that.  Let me try again,
> I will be as concise as I can.
> 
> Current custom attributes attached to the platform device are:
> 
>     /sys/bus/platform/devices/fujitsu-laptop
>     `- brightness_changed [*]
>     `- dock
>     `- lcd_level [*]
>     `- lid
>     `- max_brightness [*]
>     `- radios
> 
> AFAICT, all four of us agree that attributes marked with an asterisk [*]
> should be removed from the platform device because they are exposed by
> the backlight device anyway and do not work correctly under certain
> circumstances.
> 
> However, Darren's question to Greg did not apply to these attributes.
> It was about the other three attributes: dock, lid and radios.
> 
> In other words, my proposal was to change this:
> 
>     /sys/bus/platform/devices/fujitsu-laptop
>     `- dock
>     `- lid
>     `- radios
> 
> into this:
> 
>     /sys/bus/acpi/devices/FUJ02E3:00
>     `- dock
>     `- lid
>     `- radios
> 
> That would enable us to completely rip the platform driver and platform
> device out of fujitsu-laptop, cutting the driver down by ca. 40 lines.
> 
> Greg objected to that, arguing that there might be userspace
> applications using these attributes under their current path.  I do not
> know of such an application.  My question to Darren was thus: do we move
> dock, lid and radios and rip the platform driver and platform device out
> of fujitsu-laptop or should these attributes rather stay where they are?

I would say just to leave them as-is, there's no harm in those 40 lines,
and you really don't want to break someone's existing setup for no good
reason.

thanks,

greg k-h

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