linux-kernel - Re: "coupled" regulator support

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: <20160718180508.GV30372@sirena.org.uk>
Date:	Mon, 18 Jul 2016 19:05:08 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	Liam Girdwood <lgirdwood@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: "coupled" regulator support

On Mon, Jul 18, 2016 at 02:44:22PM +0800, Jisheng Zhang wrote:

> v1 and v2 and both valid voltages, but here we have an explicit limitation:
> we must take the "regulator shared" fact into consideration. Let's assume
> the voltage is at v2, devA is not busy now, it wants to scale down freq, then
> scale down voltage to v1, but if devB hasn't call for setting voltage to
> v1, we can't scale down voltage now, we need to wait for devB sending out
> the voltage scaling down request when it is not busy in future some time.
> Obviously, the last user will succeed to scale down the voltage.

> My solution is
> to extend regulator_check_consumers() to check whether all consumers agree
> to scaling down voltage or not.

I'm not sure I 100% follow your explanation above - it still sounds like
a normal shared regulator situation.  In general I'm really unsure how
this sort of scheme is expected to work.  It seems like in a lot of
cases there will be some other constraints in play (like needing to do
frequency updates as part of the sequence) which can't be handled purely
in the regulator API and/or that the DVFS driver ought to be able to use
notifiers to discover when actual changes have happened and handle
things in their own code.  But like I say I don't 100% follow what's new
in your example so I may be missing something.

Download attachment "signature.asc" of type "application/pgp-signature" (474 bytes)