linux-kernel - Re: [PATCH v5 05/14] clk: Add generic driver for Maxim PMIC clocks

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:	Wed, 02 Jul 2014 12:19:57 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Cc:	Mike Turquette <mturquette@...aro.org>,
	Yadwinder Singh Brar <yadi.brar01@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Doug Anderson <dianders@...omium.org>,
	Olof Johansson <olof@...om.net>,
	Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
	Daniel Stone <daniels@...labora.com>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	devicetree <devicetree@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 05/14] clk: Add generic driver for Maxim PMIC clocks

On śro, 2014-07-02 at 12:13 +0200, Javier Martinez Canillas wrote:
> Hello Mike,
> 
> On 07/01/2014 07:26 PM, Mike Turquette wrote:
> > Quoting Yadwinder Singh Brar (2014-06-29 21:01:36)
> >> Hi Javier,
> >> 
> >> On Thu, Jun 26, 2014 at 11:45 PM, Javier Martinez Canillas
> >> <javier.martinez@...labora.co.uk> wrote:
> >> > Maxim Integrated Power Management ICs are very similar with
> >> > regard to their clock outputs. Most of the clock drivers for
> >> > these chips are duplicating code and are simpler enough that
> >> > can be converted to use a generic driver to consolidate code
> >> > and avoid duplication.
> >> >
> >> > Signed-off-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
> >> > Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> >> > ---
> >> >
> >> > Changes since v4:
> >> >  - Return recalc 0 if clock isn't enabled in Suggested by Yadwinder Singh Brar.
> >> >
> >> 
> >> It seems you didn't implement or posted same patch again :) .
> >> 
> >> > Changes since v3:
> >> >  - Add current copyright information. Suggested by Krzysztof Kozlowski
> >> >  - Do a single allocation for struct max_gen_clk. Suggested by Krzysztof Kozlowski
> >> >  - Add EXPORT_SYMBOL() for exported symbols. Suggested by Krzysztof Kozlowski
> >> >
> >> >  drivers/clk/Kconfig       |   3 +
> >> >  drivers/clk/Makefile      |   1 +
> >> >  drivers/clk/clk-max-gen.c | 195 ++++++++++++++++++++++++++++++++++++++++++++++
> >> >  drivers/clk/clk-max-gen.h |  32 ++++++++
> >> >  4 files changed, 231 insertions(+)
> >> >  create mode 100644 drivers/clk/clk-max-gen.c
> >> >  create mode 100644 drivers/clk/clk-max-gen.h
> >> >
> >> 
> >> [ .. ]
> >> 
> >> > +
> >> > +static unsigned long max_gen_recalc_rate(struct clk_hw *hw,
> >> > +                                        unsigned long parent_rate)
> >> > +{
> >> > +       return 32768;
> >> > +}
> >> 
> >> Its still same here.
> > 
> > Changing this would be a new behavior. I do not know of any other clock
> > drivers that conditionally returns a rate of 0 based on whether or not
> > the clock is gated.
> > 
> 
> After Yadwinder feedback I searched for clock drivers that returned 0 when the
> clock was not enabled/prepared and found for example drivers/clk/clk-s2mps11.c:
> 
> 
> static unsigned long s2mps11_clk_recalc_rate(struct clk_hw *hw,
>                                              unsigned long parent_rate)
> {
>         struct s2mps11_clk *s2mps11 = to_s2mps11_clk(hw);
>         if (s2mps11->enabled)
>                 return 32768;
>         else
>                 return 0;
> }
> 
> > It is also buggy since calls to clk_enable and clk_disable do not invoke
> > .recalc_rate, so the rate of your clock would not be updated from the
> > framework's perspective until some later point where you call
> > clk_set_rate or something.
> >
> 
> s2ps11->enabled is set in the driver's clk_ops .prepare and .unprepare function
> handlers and calls to clk_prepare and clk_unprepare also don't seems to invoke
> .recalc_rate so I guess that driver is wrong as well and should just return the
> clock rate unconditionally?

The s2mps11 may be not a best example for proper clock driver :).
Karol Wrona already sent a patch for s2mps11:
https://lkml.org/lkml/2014/7/1/389


Best regards,
Krzysztof

> 
> > If your driver needs to know whether or not the clock is enabled then we
> > could introduce a new bool clk_is_enabled(struct clk *clk); to clk.h,
> > but I'd rather not do that. Instead if a driver needs a clock then it
> > calls clk_enable on it without any knowledge about the internal state of
> > the clock enable_count.
> > 
> > Regards,
> > Mike
> >
> 
> Thanks a lot for the explanation, I'll revert that change then and return the
> clock rate unconditionally on the next version of the patch-set.
> 
> Best regards,
> Javier

--
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/