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

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Message-ID: <14287352.RDIVbhacDa@senjougahara>
Date: Wed, 27 Aug 2025 19:36:40 +0900
From: Mikko Perttunen <mperttunen@...dia.com>
To: 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>, Svyatoslav <clamor95@...il.com>
Cc: 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

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.

> >Cheers,
> >Mikko