[PATCH 20/22] staging: media: Add support for the Allwinner A31 ISP

[Maxime Ripard]

On Fri, Sep 10, 2021 at 08:41:45PM +0200, Paul Kocialkowski wrote:
> Some Allwinner platforms come with an Image Signal Processor, which
> supports various features in order to enhance and transform data
> received by image sensors into good-looking pictures. In most cases,
> the data is raw bayer, which gets internally converted to RGB and
> finally YUV, which is what the hardware produces.
> 
> This driver supports ISPs that are similar to the A31 ISP, which was
> the first standalone ISP found in Allwinner platforms. Simpler ISP
> blocks were found in the A10 and A20, where they are tied to a CSI
> controller. Newer generations of Allwinner SoCs (starting with the
> H6, H616, etc) come with a new camera subsystem and revised ISP.
> Even though these previous and next-generation ISPs are somewhat
> similar to the A31 ISP, they have enough significant differences to
> be out of the scope of this driver.
> 
> While the ISP supports many features, including 3A and many
> enhancement blocks, this implementation is limited to the following:
> - V3s (V3/S3) platform support;
> - Bayer media bus formats as input;
> - Semi-planar YUV (NV12/NV21) as output;
> - Debayering with per-component gain and offset configuration;
> - 2D noise filtering with configurable coefficients.
> 
> Since many features are missing from the associated uAPI, the driver
> is aimed to integrate staging until all features are properly
> described.

We can add new features/interfaces to a !staging driver. Why do you
think staging is required?

> On the technical side, it uses the v4l2 and media controller APIs,
> with a video node for capture, a processor subdev and a video node
> for parameters submission. A specific uAPI structure and associated
> v4l2 meta format are used to configure parameters of the supported
> modules.

This meta format needs to be documented

Maxime
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