linux-kernel - Re: [PATCH 0/2] Add Omnivision OV4689 image sensor driver

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Message-ID: <87zgg530ht.fsf@gmail.com>
Date:   Mon, 15 Aug 2022 19:59:14 +0300
From:   Mikhail Rudenko <mike.rudenko@...il.com>
To:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Mikhail Rudenko <mike.rudenko@...il.com>
Subject: Re: [PATCH 0/2] Add Omnivision OV4689 image sensor driver

Gentle ping. Still waiting for any [2/2] review. Should I resend?


On 2022-07-12 at 17:19 +03, Mikhail Rudenko <mike.rudenko@...il.com> wrote:
> Hello,
>
> this series implements support for Omnivision OV4689 image
> sensor. The Omnivision OV4689 is a high performance, 1/3-inch, 4
> megapixel image sensor. Ihis chip supports high frame rate speeds up
> to 90 fps at 2688x1520 resolution. It is programmable through an I2C
> interface, and sensor output is sent via 1/2/4 lane MIPI CSI-2
> connection.
>
> The driver is based on Rockchip BSP kernel [1]. It implements 4-lane CSI-2
> and single 2688x1520 @ 30 fps mode. The driver was tested on Rockchip
> 3399-based FriendlyElec NanoPi M4 board with MCAM400 camera module.
>
> While porting the driver, I stumbled upon two issues:
>
> (1) In the original driver, horizontal total size (HTS) was set to a
> value (2584) lower then the frame width (2688), resulting in negative
> hblank. In this driver, I increased HTS to 2688, but fps dropped from
> 29.88 to 28.73. What is the preferred way to handle this?
>
> (2) The original driver exposes analog gain range 0x0 - 0x7ff, but the
> gain is not linear across that range. Instead, it is piecewise linear
> (and discontinuous). 0x0-0xff register values result in 0x-2x gain,
> 0x100-0x1ff to 0x-4x, 0x300-0x3ff to 0x-8x, and 0x700-0x7ff to 0x-16x,
> with more linear segments in between. Rockchip's camera engine code
> chooses one of the above segments depenging on the desired gain
> value. The question is, how should we proceed keeping in mind
> libcamera use case? Should the whole 0x0-0x7ff be exposed as-is and
> libcamera will do the mapping, or the driver will do the mapping
> itself and expose some logical gain units not tied to the actual gain
> register value? Meanwhile, this driver conservatively exposes only
> 0x0-0xf8 gain register range.
>
> [1] https://github.com/rockchip-linux/kernel/blob/develop-4.19/drivers/media/i2c/ov4689.c
>
> Mikhail Rudenko (2):
>   media: dt-bindings: media: i2c: document OV4689 DT bindings
>   media: i2c: add support for ov4689
>
>  .../bindings/media/i2c/ovti,ov4689.yaml       | 122 +++
>  MAINTAINERS                                   |   8 +
>  drivers/media/i2c/Kconfig                     |  14 +
>  drivers/media/i2c/Makefile                    |   1 +
>  drivers/media/i2c/ov4689.c                    | 899 ++++++++++++++++++
>  5 files changed, 1044 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/media/i2c/ovti,ov4689.yaml
>  create mode 100644 drivers/media/i2c/ov4689.c


--
Best regards,
Mikhail Rudenko