linux-kernel - Re: [PATCH] clockevents: Add (missing) default case for switch blocks

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: <20150220093659.GA23469@gmail.com>
Date:	Fri, 20 Feb 2015 10:36:59 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linaro-kernel@...ts.linaro.org,
	Kevin Hilman <khilman@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	linaro-networking@...aro.org, Steven Miao <realmz6@...il.com>,
	Mark Salter <msalter@...hat.com>,
	Michal Simek <monstr@...str.eu>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Ley Foon Tan <lftan@...era.com>,
	Jonas Bonn <jonas@...thpole.se>,
	"David S. Miller" <davem@...emloft.net>,
	Jeff Dike <jdike@...toit.com>,
	Guan Xuetao <gxt@...c.pku.edu.cn>
Subject: Re: [PATCH] clockevents: Add (missing) default case for switch blocks


* Peter Zijlstra <peterz@...radead.org> wrote:

> > So this whole approach looks fragile for several reasons:
> > 
> >    - 'mode setting' callbacks are just bad by design
> >      because they mix several functions into the same entry
> >      point, complicating the handler functions 
> >      unnecessarily. We should reduce complexity, not expand 
> >      on it.
> > 
> >    - now by adding 'default' you hide from drivers the
> >      ability to easily discover whether it has been updated
> >      to some new core clockevents mode setting feature or
> >      not.
> 
> So this patch was a follow on from bd624d75db21 
> ("clockevents: Introduce mode specific callbacks").
> 
> That patch changes the set_mode() interface; and provides 
> per mode functions.

So why is a 'default' mode needed then? It makes the 
addition of new modes to the legacy handler easier, which 
looks backwards.

> New (and updated) drivers should not use ->set_mode() 
> anymore, but it was felt that we do not want to go do 
> flag day changes.

I fully agree that we don't want flag day changes, but make 
it really apparent that it's an obsolete interface:

  - rename it to set_mode_obsolete()

  - try to convert as many of the easy cases as possible - 
    the overwhelming majority of mode setting functions 
    look reasonably simple.

  - get rid of the mode enum in the core, and rename the 
    mode bits to CLOCK_EVT_MODE_OBSOLETE_XXX.

etc.

> And it allows for adding optional modes; not every driver 
> needs to go implement all mode functions if there is a 
> sane default action.
> 
> But it does mean we need to be able to add values to the 
> enum.

So I'm confused: if we are using proper callbacks (like my 
example outlined) , why is a 'mode enum' needed at all?

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/