linux-kernel - Re: [PATCH v2 4/4] clk: dt: Introduce always-on clock domain documentation

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:	Thu, 19 Feb 2015 11:35:58 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Rob Herring <robherring2@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>, kernel@...inux.com,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] clk: dt: Introduce always-on clock domain documentation

Hi Lee,

On Thu, Feb 19, 2015 at 11:28 AM, Lee Jones <lee.jones@...aro.org> wrote:
> On Thu, 19 Feb 2015, Geert Uytterhoeven wrote:
>> On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@...aro.org> wrote:
>> > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote:
>> >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@...aro.org> wrote:
>> >> >> What kind of clocks are these? What do they control?
>> >> >> Memory controllers? Bus controllers?
>> >> >>
>> >> >> They must control some device(s), so there should be one or more device
>> >> >> nodes in DT that reference these clocks.
>> >> >> As soon as that information is in DT, support can be added to Linux to
>> >> >> make sure the "critical" clocks stay enabled, either through a real driver,
>> >> >> or through platform code.
>> >> >
>> >> > Some do, some don't.  For instance, we have one clock which controls
>> >> > SPI and I2C that must not be turned off.  We discovered this then when
>> >> > a suspend was attempted and the board refused to resume.  This clock
>> >> > also runs one of the critical interconnects that runs from the a9.  It
>> >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C
>> >> > drivers because the same IP on another board might be controlled by a
>> >> > different clock which is able to be gated.
>> >> >
>> >> > There are also clocks which control other interconnects that are not
>> >> > connected to any device drivers.  If we fail to take references for
>> >> > them before clk_disable_unused() is called, again the board hangs.  We
>> >> > even lose JTAG support.
>> >>
>> >> Interconnects are buses. Can't you represent those buses in the DT
>> >> hierarchy, and give them clocks properties?
>> >
>> > So instead of this nice succinct, simple, cover all bases
>> > (interconnects was just an example, there are bound to be others),
>> > generic framework, you are suggesting to write drivers for devices
>> > which other than "don't turn my clocks off", Linux can't actually see
>> > or control?
>>
>> DT describes the hardware, not behavior.
>
> Okay so ...
>
> /*
>  * ICNs are not visible/controllable in Linux, but references to their
>  * clocks must be obtained and retained or the platform will become
>  * irrecoverably unresponsive.
>  */
> interconnects@0 {
>        compatible = "always-on-clk-domain";

st,...flexgen...

>        clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>,
>                 <&clk_s_c0_flexgen CLK_ICN_LMI>,
>                 <&clk_s_c0_flexgen CLK_ICN_CPU>,
>                 <&clk_s_c0_flexgen CLK_TX_ICN_DMU>;
> };

And then you can have platform code that binds against st,...flexgen...,
and enables all referenced clocks.

Alternatively, if you have power domains, you can add a reference to
the power domain, and let the power domain driver handle it.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
--
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/