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From: Maxime Ripard <maxime@cerno.tech>
To: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc: linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-phy@lists.infradead.org, linux-clk@vger.kernel.org,
	linux-staging@lists.linux.dev, Yong Deng <yong.deng@magewell.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Hans Verkuil <hans.verkuil@cisco.com>,
	Chen-Yu Tsai <wens@csie.org>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Helen Koike <helen.koike@collabora.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH 15/22] media: sunxi: Remove the sun6i-csi driver implementation
Date: Mon, 13 Sep 2021 10:17:07 +0200	[thread overview]
Message-ID: <20210913081707.3pjcfuwan46pbdep@gilmour> (raw)
In-Reply-To: <20210910184147.336618-16-paul.kocialkowski@bootlin.com>

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On Fri, Sep 10, 2021 at 08:41:40PM +0200, Paul Kocialkowski wrote:
> As described in the commit adding support for the new sun6i-csi driver,
> a complete rewrite was necessary to support the Allwinner A31 ISP as
> well as fix a number of issues with the current implementation.
> 
> Farewell and thanks for all the pixels!
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

For completeness, this is what the other commit log mentions:

> While adapting the sun6i-csi driver for MIPI CSI-2 support was
> possible, it became clear that adding support for the ISP required
> very heavy changes to the driver which were quite hard to break down
> into a series of subsequent changes.

> The first major difficulty comes from the lack of v4l2 subdev that
> acts a bridge, separate from the video node representing the DMA
> engine. To support the ISP, only parts of the hardware must be
> configured (excluding aspects related to the DMA output), which made
> the separation a hard requirement.

> Another significant difficulty was the specific dance that is required
> to have both the ISP and CSI device be part of the same media device.
> Because the ISP and CSI are two different hardware blocks, they have
> two distinct drivers that will each try to register their own v4l2
> and media devices, resulting in two distinct pipelines. When the ISP
> is in use, we actually want the CSI driver to register with the ISP's
> v4l2 and media devices while keeping the ability to register its own
> when the ISP is not in use. This is done by:
> 1. Having the CSI driver check whether the ISP is available, using
>    sun6i_csi_isp_detect();
> 2. If not, it can register when its own async subdevs are ready, using
>    sun6i_csi_v4l2_complete();
> 3. If so, it will register its bridge as an async subdev which will
>    be picked-up by the ISP driver (from the fwnode graph link);
> 4. When the subdev becomes bound to the ISP's v4l2 device, we can
>    then access that device (and the associated media device) to
>    complete registration of the capture video node, using
>    sun6i_csi_isp_complete();
> Besides the logic rework, other issues were identified and resolved:
> - The sync mechanism for buffer flipping was based on the frame done
>   interrupt, which is too late (next frame is already being processed).
>   This lead to requiring 3 buffers to start and writing two addresses
>   when starting. Using vsync as a sync point seems to be the correct
>   approach and allows using only two buffers without tearing;
> - Using devm_regmap_init_mmio_clk was incorrect since the reset also
>   comes into play;
> - Some register definitions were inverted compared to their actual
>   effect (which was inherited from the Allwinner documentation and
>   code): comments were added where relevant;
> - The deprecated v4l2_async_notifier_parse_fwnode_endpoints() helper
>   is no longer used by the driver;

With that being said, NAK.

Having heavy changes to a driver is completely fine, and is kind of
expected really with such a big change. Breaking all possibility of
bisection and throwing away years of stabilization and maintenance
isn't.

And all those small bug fixes you mention at the end are just that:
small bug fixes that can be done on the current driver just fine too.

Maxime

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  reply	other threads:[~2021-09-13  8:17 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 18:41 [PATCH 00/22] Allwinner A31/A83T MIPI CSI-2 Support and A31 ISP Support Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 01/22] clk: sunxi-ng: v3s: Make the ISP PLL clock public Paul Kocialkowski
2021-09-13  7:54   ` Maxime Ripard
2021-09-13  8:53     ` Paul Kocialkowski
2021-09-16 16:30       ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 02/22] ARM: dts: sun8i: v3s: Parent the CSI module clock to the ISP PLL Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 03/22] dt-bindings: sun6i-a31-mipi-dphy: Add optional direction property Paul Kocialkowski
2021-09-13  8:00   ` Maxime Ripard
2021-09-14  7:39     ` Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 04/22] phy: allwinner: phy-sun6i-mipi-dphy: Support D-PHY Rx mode for MIPI CSI-2 Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 05/22] dt-bindings: media: sun6i-a31-csi: Add MIPI CSI-2 input port Paul Kocialkowski
2021-09-13  8:09   ` Maxime Ripard
2021-09-14  7:43     ` Paul Kocialkowski
2021-09-14 12:06       ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 06/22] dt-bindings: media: Add Allwinner A31 MIPI CSI-2 bindings documentation Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 07/22] media: sunxi: Add support for the A31 MIPI CSI-2 controller Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 08/22] MAINTAINERS: Add entry for the Allwinner A31 MIPI CSI-2 bridge driver Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 09/22] ARM: dts: sun8i: v3s: Add nodes for MIPI CSI-2 support Paul Kocialkowski
2021-09-11  2:32   ` Samuel Holland
2021-09-13  7:44     ` Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 10/22] dt-bindings: media: Add Allwinner A83T MIPI CSI-2 bindings documentation Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 11/22] media: sunxi: Add support for the A83T MIPI CSI-2 controller Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 12/22] MAINTAINERS: Add entry for the Allwinner A83T MIPI CSI-2 bridge Paul Kocialkowski
2021-09-10 18:41 ` [PATCH NOT FOR MERGE 13/22] ARM: dts: sun8i: a83t: Add MIPI CSI-2 controller node Paul Kocialkowski
2021-09-11  2:53   ` Chen-Yu Tsai
2021-09-13  7:45     ` Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 14/22] ARM: dts: sun8i: a83t: bananapi-m3: Enable MIPI CSI-2 with OV8865 Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 15/22] media: sunxi: Remove the sun6i-csi driver implementation Paul Kocialkowski
2021-09-13  8:17   ` Maxime Ripard [this message]
2021-09-14  8:04     ` Paul Kocialkowski
2021-09-15 19:51       ` Sakari Ailus
2021-09-10 18:41 ` [PATCH 16/22] media: sunxi: Introduce a rewritten sun6i-csi driver Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 17/22] dt-bindings: media: Add Allwinner A31 ISP bindings documentation Paul Kocialkowski
2021-09-13  8:18   ` Maxime Ripard
2021-09-14  7:44     ` Paul Kocialkowski
2021-09-14 12:07       ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 18/22] dt-bindings: media: sun6i-a31-csi: Add ISP output port Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 19/22] soc: sunxi: mbus: Add A31 ISP compatibles to the list Paul Kocialkowski
2021-09-11  2:36   ` Samuel Holland
2021-09-13  7:45     ` Paul Kocialkowski
2021-09-13  8:32       ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 20/22] staging: media: Add support for the Allwinner A31 ISP Paul Kocialkowski
2021-09-13  8:31   ` Maxime Ripard
2021-09-14  7:50     ` Paul Kocialkowski
2021-09-14 11:11       ` Laurent Pinchart
2021-09-14 11:48         ` Maxime Ripard
2021-09-10 18:41 ` [PATCH 21/22] MAINTAINERS: Add entry for the Allwinner A31 ISP driver Paul Kocialkowski
2021-09-10 18:41 ` [PATCH 22/22] ARM: dts: sun8i: v3s: Add support for the ISP Paul Kocialkowski

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