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

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Date:   Mon, 6 Mar 2017 15:46:46 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Peter De Schrijver <pdeschrijver@...dia.com>
CC:     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@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: tegra: mark TEGRA210_CLK_DBGAPB as always on


On 06/03/17 14:28, Peter De Schrijver 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.

Yes I understand, but if we just enable it, people may assume that this
clock always needs to be on without knowing that it is optional and it
is safe to disable if you are not using JTAG.

So at a minimum we should have a comment about this. What about adding a
CONFIG_TEGRA_ENABLE_JTAG option? I would be ok with the default being
enabled.

Cheers
Jon

-- 
nvpublic