linux-kernel - Re: [PATCH] clk: tegra: mark TEGRA210_CLK

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Date:   Wed, 8 Mar 2017 09:23:07 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Stephen Warren <swarren@...dotorg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Alexandre Courbot <gnurou@...il.com>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-tegra@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: tegra: mark TEGRA210_CLK_DBGAPB as always on

Hi Jon,

On Tue, Mar 7, 2017 at 9:27 PM, Jon Hunter <jonathanh@...dia.com> wrote:
> On 06/03/17 15:53, Geert Uytterhoeven wrote:
>> On Mon, Mar 6, 2017 at 3:28 PM, Peter De Schrijver
>> <pdeschrijver@...dia.com> wrote:
>>> On Mon, Mar 06, 2017 at 09:58:29AM +0000, Jon Hunter wrote:
>>>> On 06/03/17 08:38, Peter De Schrijver wrote:
>>>>> On Thu, Mar 02, 2017 at 05:56:49PM +0000, Jon Hunter wrote:
>>>>>> On 28/02/17 15:19, Peter De Schrijver wrote:
>>>>>>> This is needed to make the JTAG debugging interface work.
>>>>>>>
>>>>>>> Signed-off-by: Peter De Schrijver <pdeschrijver@...dia.com>
>>>>>>> ---
>>>>>>>  drivers/clk/tegra/clk-tegra210.c | 1 +
>>>>>>>  1 file changed, 1 insertion(+)
>>>>>>>
>>>>>>> diff --git a/drivers/clk/tegra/clk-tegra210.c b/drivers/clk/tegra/clk-tegra210.c
>>>>>>> index 9a2512a..708f5f1 100644
>>>>>>> --- a/drivers/clk/tegra/clk-tegra210.c
>>>>>>> +++ b/drivers/clk/tegra/clk-tegra210.c
>>>>>>> @@ -2680,6 +2680,7 @@ static void tegra210_cpu_clock_resume(void)
>>>>>>>   { TEGRA210_CLK_EMC, TEGRA210_CLK_CLK_MAX, 0, 1 },
>>>>>>>   { TEGRA210_CLK_MSELECT, TEGRA210_CLK_CLK_MAX, 0, 1 },
>>>>>>>   { TEGRA210_CLK_CSITE, TEGRA210_CLK_CLK_MAX, 0, 1 },
>>>>>>> + { TEGRA210_CLK_DBGAPB, TEGRA210_CLK_CLK_MAX, 0, 1 },
>>>>>>>   { TEGRA210_CLK_TSENSOR, TEGRA210_CLK_CLK_M, 400000, 0 },
>>>>>>>   { TEGRA210_CLK_I2C1, TEGRA210_CLK_PLL_P, 0, 0 },
>>>>>>>   { TEGRA210_CLK_I2C2, TEGRA210_CLK_PLL_P, 0, 0 },
>>>>>>
>>>>>> Should there be some dependency on say CONFIG_DEBUG_KERNEL? I am not
>>>>>> sure we always want this on for all cases.
>>>>>
>>>>> Why would you not want it to be always on?
>>>>
>>>> Purely for power reasons. I do not know how much power keeping this
>>>
>>> I don't expect it to be significant but I don't have any numbers.
>>>
>>>> clock running consumes, but I don't like the idea of clocks running all
>>>> the time when they are not needed.
>>>
>>> Problem is that in this case there is no easy way to determine if the clock
>>> needs to be on.
>>
>> I had a similar issue with SH-Mobile AG5, where the power domain containing
>> the JTAG interface is powered down.
>>
>> [DEBUG] ARM: dts: sh73a0: Add minimal device node for Coresight-ETM
>> https://patchwork.kernel.org/patch/8151511/
>>
>> Want to debug? Apply patch. I know it's not ideal...
>
> Why don't you apply the patch and just keep the node disabled by default?

Thanks, good idea!

Then I first have to make get_special_pds() skip disabled nodes...

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