linux-kernel - Re: [PATCH v1 01/19] clk: tegra: init CSUS clock for Tegra20 and Tegra30

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Message-ID: <CAPVz0n0kCBAh7W0R766A_dXbcM3E=EoSXemuc0_rOm+Qch-a+Q@mail.gmail.com>
Date: Wed, 27 Aug 2025 13:45:28 +0300
From: Svyatoslav Ryhel <clamor95@...il.com>
To: Mikko Perttunen <mperttunen@...dia.com>
Cc: Thierry Reding <thierry.reding@...il.com>, Thierry Reding <treding@...dia.com>, 
	Jonathan Hunter <jonathanh@...dia.com>, Sowjanya Komatineni <skomatineni@...dia.com>, 
	Luca Ceresoli <luca.ceresoli@...tlin.com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Peter De Schrijver <pdeschrijver@...dia.com>, Prashant Gaikwad <pgaikwad@...dia.com>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Dmitry Osipenko <digetx@...il.com>, Charan Pedumuru <charan.pedumuru@...il.com>, 
	linux-media@...r.kernel.org, linux-tegra@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org, 
	linux-staging@...ts.linux.dev
Subject: Re: [PATCH v1 01/19] clk: tegra: init CSUS clock for Tegra20 and Tegra30

ср, 27 серп. 2025 р. о 13:36 Mikko Perttunen <mperttunen@...dia.com> пише:
>
> On Wednesday, August 27, 2025 1:32 PM Svyatoslav wrote:
> > 27 серпня 2025 р. 07:09:45 GMT+03:00, Mikko Perttunen
> <mperttunen@...dia.com> пише:
> > >On Tuesday, August 19, 2025 9:16 PM Svyatoslav Ryhel wrote:
> > >> CSUS clock is required to be enabled on camera device configuration or
> > >> else camera module refuses to initiate properly.
> > >>
> > >> Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
> > >> ---
> > >>
> > >>  drivers/clk/tegra/clk-tegra20.c | 1 +
> > >>  drivers/clk/tegra/clk-tegra30.c | 1 +
> > >>  2 files changed, 2 insertions(+)
> > >>
> > >> diff --git a/drivers/clk/tegra/clk-tegra20.c
> > >> b/drivers/clk/tegra/clk-tegra20.c index 551ef0cf0c9a..42f8150c6110 100644
> > >> --- a/drivers/clk/tegra/clk-tegra20.c
> > >> +++ b/drivers/clk/tegra/clk-tegra20.c
> > >> @@ -1043,6 +1043,7 @@ static struct tegra_clk_init_table init_table[] = {
> > >>
> > >>    { TEGRA20_CLK_GR3D, TEGRA20_CLK_PLL_C, 300000000, 0 },
> > >>    { TEGRA20_CLK_VDE, TEGRA20_CLK_PLL_C, 300000000, 0 },
> > >>    { TEGRA20_CLK_PWM, TEGRA20_CLK_PLL_P, 48000000, 0 },
> > >>
> > >> +  { TEGRA20_CLK_CSUS, TEGRA20_CLK_CLK_MAX, 6000000, 1 },
> > >>
> > >>    /* must be the last entry */
> > >>    { TEGRA20_CLK_CLK_MAX, TEGRA20_CLK_CLK_MAX, 0, 0 },
> > >>
> > >>  };
> > >>
> > >> diff --git a/drivers/clk/tegra/clk-tegra30.c
> > >> b/drivers/clk/tegra/clk-tegra30.c index 82a8cb9545eb..70e85e2949e0 100644
> > >> --- a/drivers/clk/tegra/clk-tegra30.c
> > >> +++ b/drivers/clk/tegra/clk-tegra30.c
> > >> @@ -1237,6 +1237,7 @@ static struct tegra_clk_init_table init_table[] = {
> > >>
> > >>    { TEGRA30_CLK_HDA, TEGRA30_CLK_PLL_P, 102000000, 0 },
> > >>    { TEGRA30_CLK_HDA2CODEC_2X, TEGRA30_CLK_PLL_P, 48000000, 0 },
> > >>    { TEGRA30_CLK_PWM, TEGRA30_CLK_PLL_P, 48000000, 0 },
> > >>
> > >> +  { TEGRA30_CLK_CSUS, TEGRA30_CLK_CLK_MAX, 6000000, 1 },
> > >>
> > >>    /* must be the last entry */
> > >>    { TEGRA30_CLK_CLK_MAX, TEGRA30_CLK_CLK_MAX, 0, 0 },
> > >>
> > >>  };
> > >
> > >I looked into what this clock does and it seems to be a gate for the CSUS
> > >pin, which provides an output clock for camera sensors (VI MCLK). Default
> > >source seems to be PLLC_OUT1. It would be good to note that on the commit
> > >message, as I can't find any documentation about the CSUS clock elsewhere.
> > >
> > >What is the 6MHz rate based on?
> >
> > 6mhz is the statistic value which I was not able to alter while testing. I
> > have tried 12mhz and 24mhz too but it remained 6mhz, so I left it 6mhz.
> > >Since this seems to be a clock consumed by the sensor, it seems to me that
> > >rather than making it always on, we could point to it in the sensor's
> > >device tree entry.
> >
> > Sensor device tree uses vi_sensor as clocks source and sensor drivers don't
> > support multiple linked clocks.
>
> AIUI vi_sensor is an internal clock so the sensor cannot be receiving it
> directly. Perhaps the sensor is actually connected to csus, and the reason we
> need to enable it is to allow the vi_sensor clock to pass through the csus
> gate?
>
> That leaves the question of why the csus pad would be muxed to vi_sensor by
> default, but perhaps there's an explanation for that.
>

>From downstream T30 sources csus and vi_sensor are always called in
pair (6MHz csus and 24MHz for vi_sensor), naturally I assumed that
latter is used as camera reference clock since most sensors has
reference clock around 24 MHz

> > >Cheers,
> > >Mikko
>
>
>
>