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

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Date:   Mon, 13 Mar 2017 12:47:20 +0200
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Jon Hunter <jonathanh@...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

On Mon, Mar 06, 2017 at 04:53:48PM +0100, Geert Uytterhoeven wrote:
> Hi Peter,
> 
> 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...
> 

Don't you always want to debug? :-)

Peter.