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]
Date:	Tue, 18 Dec 2012 08:47:11 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Chao Xie <xiechao.mail@...il.com>
Cc:	mturquette@...aro.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, haojian.zhuang@...il.com
Subject: Re: common clock framwork: clk_set_rate issue

On Tue, Dec 18, 2012 at 10:19:21AM +0800, Chao Xie wrote:
> On Tue, Dec 18, 2012 at 4:19 AM, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> > On Thu, Dec 06, 2012 at 10:52:03AM +0800, Chao Xie wrote:
> >> hi
> >> When develop the clk drivers for SOCs based on common clock framework.
> >> I met a issue.
> >> For example there is a uart device, it's function clock comes from a
> >> divider, and the divider's parent is a mux. It means
> >>
> >> MUX --> DIV --> UART
> >>
> >> As we know that UART can work at low baudrate for a terminal, while it
> >> can also connect to GPS module which needs a high rate. So the MUX
> >> will provide two clock source, a low clock rate and high clock rate.
> >>
> >> The MUX clk driver clk-mux.c does not implement a ->round_rate callbacks.
> >> It means that when uart driver is used for a GPS and it want to change
> >> it clock, the driver will call clk_set_rate(); clk_set_rate will loop
> >> upward to DIV, and DIV will try to set its divider, and it need loop
> >> upward to MUX.
> >> In fact the current clk drivers have some issue.
> >> MUX clk driver should provide the round_rate callback, it then can
> >> provide a new_rate. It means that in clk_calc_subtree MUX can switch
> >> the clock source.
> >
> > It's not that simple. The input clocks to a mux may not only differ in
> > their rate but can also have other different properties, like for
> > example one input may be always present whereas another input only runs
> > when the CPU is in run mode.
> >
> > It may be a possibility to add a flag to the mux to explicitely
> > allow reparenting on a rate change.
> >
> There is already a flag to do it.
> CLK_SET_RATE_PARENT

That flag has another meaning. It means that a clock is allowed to
change the parents rate when a rate change is requested. What I meant
is a flag that allows a mux to change its parent when a rate change is
requested.
 
> if the mux does not want to changes the input for clk_set_rate called
> by its child, it can clear this flag.
> The question is whether we need add the round_rate/recalc_rate for MUX
> type of clock? Is there any special issue about it that why current
> MUX implementation does not have these callbacks?

They currently do not need these callbacks. When a clock does not have
round_rate propagates up to the parent if CLK_SET_RATE_PARENT is set or
it returns the parents rate if this flag is not set. The situation with
set_rate is similar.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
--
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/

Powered by blists - more mailing lists