linux-kernel - Re: [PATCH] clk: clk_register: Correctly initialize enable

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: <56BB82A8.8010701@nvidia.com>
Date:	Wed, 10 Feb 2016 13:34:16 -0500
From:	Rhyland Klein <rklein@...dia.com>
To:	Emilio López <emilio@...pez.com.ar>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>
CC:	<linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: clk_register: Correctly initialize enable_count

On 2/9/2016 9:56 PM, Emilio López wrote:
> Hi,
> 
> El 09/02/16 a las 19:48, Rhyland Klein escribió:
>> When clocks are registered, they could be enabled already in
>> hardware. As of now, the enable count will start at 0. When this
>> happens, it means a clock is enabled and the framework doesn't know
>> that, so it will always report it as disabled.
> 
> Keep in mind that during the boot process, towards the end, unused
> clocks get disabled, so the state remains in sync. If suddenly the
> enable_count on unused clocks is not 0, this will break and unused
> clocks will remain on, wasting power.

Hmm, I had misread the logic in clk_disable_unused_subtree(), namely I
inverted the check on enable_count when I was looking at it. It does
seem like it would take care of the clocks I was referring to.

> 
> http://lxr.free-electrons.com/source/drivers/clk/clk.c#L244
> 
> What issue were you having that prompted you to write this patch?

I ran into the situation where a peripheral clock was enabled before the
kernel loaded, and I was trying to disable it in the clk-tegra210
driver. Calling clk_disable() won't work, as the clock doesn't have an
enable_count.

I do think that the clk_disable_unused_subtree() should pick up the
slack, but I was trying to disable it before the cleanup code to remove
unused clocks ran.

I think you are right and the clean up code should cover the situation I
was looking at.

Thanks.
-rhyland

-- 
nvpublic