From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <pdeschrijver@nvidia.com>
Date: Mon, 13 Mar 2017 12:47:20 +0200
From: Peter De Schrijver <pdeschrijver@nvidia.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
CC: Jon Hunter <jonathanh@nvidia.com>, Prashant Gaikwad <pgaikwad@nvidia.com>,
	Michael Turquette <mturquette@baylibre.com>, Stephen Boyd
	<sboyd@codeaurora.org>, Stephen Warren <swarren@wwwdotorg.org>, "Thierry
 Reding" <thierry.reding@gmail.com>, Alexandre Courbot <gnurou@gmail.com>,
	linux-clk <linux-clk@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] clk: tegra: mark TEGRA210_CLK_DBGAPB as always on
Message-ID: <20170313104720.GU26640@tbergstrom-lnx.Nvidia.com>
References: <1488295191-24038-1-git-send-email-pdeschrijver@nvidia.com>
 <4cf40c25-2ce9-737c-9ccb-06bc2cdb61d7@nvidia.com>
 <20170306083835.GF26640@tbergstrom-lnx.Nvidia.com>
 <6d4dd315-cab6-189d-f383-fb7523fc31bd@nvidia.com>
 <20170306142850.GJ26640@tbergstrom-lnx.Nvidia.com>
 <CAMuHMdWD5Pw4BfH7YMY5hnxGbib=8zqUrHrG+GHXquRjjSZ+gA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
In-Reply-To: <CAMuHMdWD5Pw4BfH7YMY5hnxGbib=8zqUrHrG+GHXquRjjSZ+gA@mail.gmail.com>
Return-Path: pdeschrijver@nvidia.com
List-ID: <linux-clk.vger.kernel.org>

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@nvidia.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@nvidia.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.