linux-kernel - Re: [PATCH v2 4/7] media: i2c: max9286: Make channel amplitude programmable

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Date:   Fri, 16 Oct 2020 11:08:37 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...il.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        kieran.bingham+renesas@...asonboard.com,
        laurent.pinchart+renesas@...asonboard.com,
        niklas.soderlund+renesas@...natech.se
Cc:     linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hyun Kwon <hyunk@...inx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: Re: [PATCH v2 4/7] media: i2c: max9286: Make channel amplitude
 programmable

Hello!

On 15.10.2020 21:27, Jacopo Mondi wrote:

> Instrument the function that configures the reverse channel with a
> programmable amplitude value.
> 
> This change serves to prepare to adjust the reverse channel amplitude
> depending on the remote end high-threshold configuration.
> 
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> ---
>   drivers/media/i2c/max9286.c | 22 ++++++++++++++++------
>   1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> index 89a7248f5c25..163e102199e3 100644
> --- a/drivers/media/i2c/max9286.c
> +++ b/drivers/media/i2c/max9286.c
> @@ -906,19 +906,29 @@ static void max9286_v4l2_unregister(struct max9286_priv *priv)
>    * Probe/Remove
>    */
>   
> -static void max9286_reverse_channel_setup(struct max9286_priv *priv)
> +static void max9286_reverse_channel_setup(struct max9286_priv *priv,
> +					  unsigned int chan_amplitude)
>   {
> +	/* Reverse channel transmission time: default to 1. */
> +	u8 chan_config = MAX9286_REV_TRF(1);
> +
>   	/*
>   	 * Reverse channel setup.
>   	 *
>   	 * - Enable custom reverse channel configuration (through register 0x3f)
>   	 *   and set the first pulse length to 35 clock cycles.
> -	 * - Increase the reverse channel amplitude to 170mV to accommodate the
> -	 *   high threshold enabled by the serializer driver.
> +	 * - Adjust reverse channel amplitude: values > 130 are programmed
> +	 *   using the additional +100mV REV_AMP_X boost flag
>   	 */
>   	max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35));
> -	max9286_write(priv, 0x3b, MAX9286_REV_TRF(1) | MAX9286_REV_AMP(70) |
> -		      MAX9286_REV_AMP_X);
> +
> +	if (chan_amplitude > 100) {
> +		/* It is not possible express values (100 < x < 130) */

    "To express", perhaps?

> +		chan_amplitude = chan_amplitude < 130
> +			       ? 30 : chan_amplitude - 100;
> +		chan_config |= MAX9286_REV_AMP_X;
> +	}
> +	max9286_write(priv, 0x3b, chan_config | MAX9286_REV_AMP(chan_amplitude));
>   	usleep_range(2000, 2500);
>   }
>   
[...]

MBR, Sergei