linux-kernel - Re: [PATCH v5 23/23] staging: media: tegra-video: add CSI support for Tegra20 and Tegra30

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Message-ID: <mzapp3ekwj3xdzqjjwkwn2hdfunf75fnd3wwxfsr5nce5guhoa@k2dgiw4sngrd>
Date: Mon, 17 Nov 2025 12:56:14 +0100
From: Thierry Reding <thierry.reding@...il.com>
To: Svyatoslav Ryhel <clamor95@...il.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Jonathan Hunter <jonathanh@...dia.com>, Sowjanya Komatineni <skomatineni@...dia.com>, 
	Luca Ceresoli <luca.ceresoli@...tlin.com>, Prashant Gaikwad <pgaikwad@...dia.com>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Mikko Perttunen <mperttunen@...dia.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jonas Schwöbel <jonasschwoebel@...oo.de>, 
	Dmitry Osipenko <digetx@...il.com>, Charan Pedumuru <charan.pedumuru@...il.com>, 
	Diogo Ivo <diogo.ivo@...nico.ulisboa.pt>, Aaron Kling <webgeek1234@...il.com>, 
	Arnd Bergmann <arnd@...db.de>, dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
	linux-clk@...r.kernel.org, linux-staging@...ts.linux.dev
Subject: Re: [PATCH v5 23/23] staging: media: tegra-video: add CSI support
 for Tegra20 and Tegra30

On Wed, Oct 22, 2025 at 05:49:30PM +0300, Svyatoslav Ryhel wrote:
> Add support for MIPI CSI device and calibration logic found in Tegra20 and
> Tegra30 SoC.
> 
> To get CSI operational, an additional syncpoint was allocated to serve as
> the CSI frame counter. Both VIP and CSI use an existing syncpoint for VI
> frame start events. That said, the frame capture function was refactored
> to reflect the addition of the CSI syncpoint, and the CSI-specific
> configuration is guarded by the presence of a passed CSI channel structure
> pointer.
> 
> The camera capture setup's configuration was reconsidered: the first two
> writes must be done before tegra_channel_set_stream for MIPI calibration
> to work properly; the third write was moved to VIP/CSI-specific functions
> since it must be source-specific; the function was placed after
> tegra_channel_set_stream so the initial sequence is preserved and expanded.
> 
> CSI configuration sequences were added based on downstream 3.1 kernel
> sources and adjusted to the existing video-tegra framework. Although
> Tegra20 and Tegra30 have the same set of configurations, they differ by
> the number of clocks used by CSI.
> 
> Dropped the software syncpoint counters in favor of reading syncpoints
> directly and passing the incremented value to the polling function. If the
> syncpoint increase fails, the PP is reset. This change should prevent
> possible race conditions.
> 
> MIPI calibration logic was registered in CSI since Tegra20 and Tegra30
> have no dedicated hardware block for these operations and use CSI. These
> calls are used for both CSI and DSI to work properly, which is why MIPI
> calibration cannot be contained within CSI. The pads passed to the
> calibration calls resemble CSI PORT_A (0), CSI PORT_B (1), DSI-A (3) and
> DSI-B (4).
> 
> Co-developed-by: Jonas Schwöbel <jonasschwoebel@...oo.de>
> Signed-off-by: Jonas Schwöbel <jonasschwoebel@...oo.de>
> Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
> ---
>  drivers/staging/media/tegra-video/csi.c     |  23 +
>  drivers/staging/media/tegra-video/csi.h     |   4 +
>  drivers/staging/media/tegra-video/tegra20.c | 620 ++++++++++++++++++--
>  drivers/staging/media/tegra-video/vi.h      |   2 -
>  drivers/staging/media/tegra-video/video.c   |   6 +
>  5 files changed, 608 insertions(+), 47 deletions(-)

Sorry, didn't realize that this was supposed to be part of the earlier
series that contains the opsification since it shows up as separate
patch series. Admittedly the numbering should've given it away... Thanks
Mikko for pointing that out.

Anyway, most of my objections remain. You can implement this here just
the same even without most of the extra churn in the prior patch. No
need for moving things to a different header, just keep adding the new
ops stuff to the existing one, which all drivers that need the
calibration functionality already include anyway (including this). Also
no need to split out the SoC specific bits from the mipi.c file since,
like I said, it's not going to grow anymore and can just remain as it
is.

Thierry

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