linux-kernel - Re: [PATCH 3/3] media: i2c: ov9282: add strobe

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Message-ID: <CAPY8ntBBiuQtKErZ1+zDD5HBwjPRdBryduuB3XnhCZAdPC88GA@mail.gmail.com>
Date: Tue, 4 Mar 2025 10:28:45 +0000
From: Dave Stevenson <dave.stevenson@...pberrypi.com>
To: Richard Leitner <richard.leitner@...ux.dev>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] media: i2c: ov9282: add strobe_timeout v4l2 control

Hi Richard

On Mon, 3 Mar 2025 at 22:59, Richard Leitner <richard.leitner@...ux.dev> wrote:
>
> Add V4L2_CID_FLASH_TIMEOUT support using the "strobe_frame_span"
> feature of the sensor. This is implemented by transforming the given µs
> value by an interpolated formula to a "span step width" value and
> writing it to register PWM_CTRL_25, PWM_CTRL_26, PWM_CTRL_27,
> PWM_CTRL_28 (0x3925, 0x3926, 0x3927, 0x3928).
>
> The maximum control value is set to the period of the current framerate.
> This must be changed to a dynamic range as soon as this driver
> implements the set_frame_interval() pad operation.
>
> All register values are based on the OV9281 datasheet v1.53 (jan 2019)
> and tested using an ov9281 VisionComponents module.
>
> Signed-off-by: Richard Leitner <richard.leitner@...ux.dev>
> ---
>  drivers/media/i2c/ov9282.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>
> diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
> index c98ba466e9aea29baff0b13578d760bf69c958c5..f7dfe8987e524b73af7e16e12567e96627b4f89a 100644
> --- a/drivers/media/i2c/ov9282.c
> +++ b/drivers/media/i2c/ov9282.c
> @@ -97,6 +97,10 @@
>  #define OV9282_REG_MIPI_CTRL00 0x4800
>  #define OV9282_GATED_CLOCK     BIT(5)
>
> +/* Flash/Strobe control registers */
> +#define OV9282_REG_FLASH_DURATION      0x3925
> +#define OV9282_FLASH_DURATION_DEFAULT  0x0000001A
> +
>  /* Input clock rate */
>  #define OV9282_INCLK_RATE      24000000
>
> @@ -193,6 +197,7 @@ struct ov9282_mode {
>   * @again_ctrl: Pointer to analog gain control
>   * @pixel_rate: Pointer to pixel rate control
>   * @flash_led_mode: Pointer to flash led mode control
> + * @flash_timeout: Pointer to flash timeout control
>   * @vblank: Vertical blanking in lines
>   * @noncontinuous_clock: Selection of CSI2 noncontinuous clock mode
>   * @cur_mode: Pointer to current selected sensor mode
> @@ -216,6 +221,7 @@ struct ov9282 {
>         };
>         struct v4l2_ctrl *pixel_rate;
>         struct v4l2_ctrl *flash_led_mode;
> +       struct v4l2_ctrl *flash_timeout;

You only access this in ov9282_set_ctrl where you already have the
struct v4l2_ctrl, so there is no need to store this in the main device
state.

  Dave

>         u32 vblank;
>         bool noncontinuous_clock;
>         const struct ov9282_mode *cur_mode;
> @@ -689,6 +695,24 @@ static int ov9282_set_ctrl_flash_led_mode(struct ov9282 *ov9282, int mode)
>                                 current_val);
>  }
>
> +static int ov9282_set_ctrl_flash_timeout(struct ov9282 *ov9282, int value)
> +{
> +       /* Calculate "strobe_frame_span" increments from a given value (µs).
> +        * This is quite tricky as "The step width of shift and span is
> +        * programmable under system clock domain.", but it's not documented
> +        * how to program this step width (at least in the datasheet available
> +        * to the author at time of writing).
> +        * The formula below is interpolated from different modes/framerates
> +        * and should work quite well for most settings.
> +        */
> +       u32 val = value * 192 / (ov9282->cur_mode->width + ov9282->hblank_ctrl->val);
> +
> +       ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION, 1, (val >> 24) & 0xff);
> +       ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION + 1, 1, (val >> 16) & 0xff);
> +       ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION + 2, 1, (val >> 8) & 0xff);
> +       return ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION + 3, 1, val & 0xff);
> +}
> +
>  /**
>   * ov9282_set_ctrl() - Set subdevice control
>   * @ctrl: pointer to v4l2_ctrl structure
> @@ -758,6 +782,9 @@ static int ov9282_set_ctrl(struct v4l2_ctrl *ctrl)
>         case V4L2_CID_FLASH_LED_MODE:
>                 ret = ov9282_set_ctrl_flash_led_mode(ov9282, ctrl->val);
>                 break;
> +       case V4L2_CID_FLASH_TIMEOUT:
> +               ret = ov9282_set_ctrl_flash_timeout(ov9282, ctrl->val);
> +               break;
>         default:
>                 dev_err(ov9282->dev, "Invalid control %d", ctrl->id);
>                 ret = -EINVAL;
> @@ -1420,6 +1447,10 @@ static int ov9282_init_controls(struct ov9282 *ov9282)
>                                                         (1 << V4L2_FLASH_LED_MODE_TORCH),
>                                                         V4L2_FLASH_LED_MODE_NONE);
>
> +       ov9282->flash_timeout = v4l2_ctrl_new_std(ctrl_hdlr, &ov9282_ctrl_ops,
> +                                                 V4L2_CID_FLASH_TIMEOUT,
> +                                                 0, 13900, 1, 8);
> +
>         ret = v4l2_fwnode_device_parse(ov9282->dev, &props);
>         if (!ret) {
>                 /* Failure sets ctrl_hdlr->error, which we check afterwards anyway */
>
> --
> 2.47.2
>
>