linux-kernel - Re: [PATCH v2 13/14] clk: shmobile: mstp: Consider "zb

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Date:	Mon, 22 Jun 2015 22:17:03 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Michael Turquette <mturquette@...libre.com>
Cc:	Geert Uytterhoeven <geert+renesas@...der.be>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-clk@...r.kernel.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 13/14] clk: shmobile: mstp: Consider "zb_clk" suitable
 for power management

Hi Mike,

On Mon, Jun 22, 2015 at 10:05 PM, Michael Turquette
<mturquette@...aro.org> wrote:

Still sending email from Linaro, which will cause me to receive an autoreply?

> Quoting Geert Uytterhoeven (2015-05-28 11:53:38)
>> Currently the CPG Clock Domain code looks for MSTP clocks to power
>> manage a device.
>>
>> Unfortunately, on R-Mobile APE6 (r8a73a4) and SH-Mobile AG5 (sh73a0),
>> the Bus State Controller (BSC) is not power-managed by an MSTP clock,
>> but by a plain CPG clock (zb_clk).  Add a special case to handle this,
>> so the clock is properly managed, and devices connected to the BSC work
>> as expected.
>>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>> ---
>> v2:
>>   - New.
>> ---
>>  drivers/clk/shmobile/clk-mstp.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/clk/shmobile/clk-mstp.c b/drivers/clk/shmobile/clk-mstp.c
>> index 619f3eccefd4884f..19e2b11953383587 100644
>> --- a/drivers/clk/shmobile/clk-mstp.c
>> +++ b/drivers/clk/shmobile/clk-mstp.c
>> @@ -258,6 +258,10 @@ int cpg_mstp_attach_dev(struct generic_pm_domain *domain, struct device *dev)
>>                                             "renesas,cpg-mstp-clocks"))
>>                         goto found;
>>
>> +               /* BSC on r8a73a4/sh73a0 uses zb_clk instead of an mstp clock*/
>> +               if (!strcmp(clkspec.np->name, "zb_clk"))
>> +                       goto found;
>
> Hello Geert,
>
> Is the driver the right place to handle this corner case? What do you
> think about linking zb_clk up to the bsc devicetree node for
> r8a73a4/sh73a0?

It already is linked:

        bsc: bus@...10000 {
                compatible = "renesas,bsc-r8a73a4", "renesas,bsc",
                    "simple-pm-bus";
                #address-cells = <1>;
                #size-cells = <1>;
               ranges = <0 0 0 0x20000000>;
               reg = <0 0xfec10000 0 0x400>;
                clocks = <&zb_clk>;
               power-domains = <&pd_c4>;
        };

        https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/r8a73a4.dtsi#n446

But without this hack in clk-mstp, the clock domain controller doesn't know
it can use this clock for power management like an ordinary mstp clock.

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
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