linux-kernel - Re: Problem with nbcon console and amba-pl011 serial port

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: <aD__pjZ_o7QMbXhC@shell.armlinux.org.uk>
Date: Wed, 4 Jun 2025 09:11:18 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: John Ogness <john.ogness@...utronix.de>
Cc: "Toshiyuki Sato (Fujitsu)" <fj6611ie@...itsu.com>,
	'Michael Kelley' <mhklinux@...look.com>,
	"pmladek@...e.com" <pmladek@...e.com>,
	'Ryo Takakura' <ryotkkr98@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Problem with nbcon console and amba-pl011 serial port

On Wed, Jun 04, 2025 at 09:50:03AM +0206, John Ogness wrote:
> You are correct. I wasn't aware that the clock framework had a usage
> counter to allow recursive calls. Sorry for the noise.

It's documented:

/**
 * clk_disable - inform the system when the clock source is no longer required.
 * @clk: clock source
 *
 * Inform the system that a clock source is no longer required by
 * a driver and may be shut down.
 *
 * May be called from atomic contexts.
 *
 * Implementation detail: if the clock source is shared between
 * multiple drivers, clk_enable() calls must be balanced by the
 * same number of clk_disable() calls for the clock source to be
 * disabled.
 */

similarly for clk_unprepare(). It has to be this way if you think about
the fact that clock sources are not unique to clock consumers, otherwise
the first clock consumer to disable a clock will disrupt other
consumers of that same clock.

It's been that way since I created the clk API, which predates CCF.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!